There are a number of factors that determine the market price for faucets, but rather than throwing out generalizations, take a look at the specifics of the California vs. other brands.
For the purposes of this comparison, let's use the most common California faucet, one I've installed plenty of : the Venice Series ($280 street price) vs. the Moen Monticello and the Delta of your choice (although the previous posters were all referring to the Delta single-control "ball-type" models.
The California faucet has a classical styling from a standard pattern that has been copied from the high end (Dornbracht) to the low end Wang-Fu chromed plastic big box specials. Stylistically, you could get something that looked similar from $50 to $1100, so why buy the California?
The plating is excellent. The base metal is brass. Many others (like your Delta) are zinc-aluminum alloy castings (Zamak). Sometimes this is referred to as "white" or "pot" metal. The advantage is that it's cheap to die-cast the parts, much more so than casting and/or machining brass. The cross handles of the California faucets are individually machined and silver soldered in place so that they don't come loose (like the Rafael ones used to do). Fit and finish of the California products I've worked with I would rate a 9 out of 10.
Let's talk about those valves. Yes, the Californias use ceramic valves. And Ceramic valves can be damaged, but it's unusual. The material is so hard that it's self-cleaning, and impervious to just about anything mineral in your water. If you try to force the thing shut on a gob of solder, yeah, you could possibly damage the insert or cartridge, but that's more your plumber's fault than a design flaw. Ceramic valves are not expensive in and of themselves, the $60 A/S Cadet had a ceramic valve, so you do the math.
Some faucets have failure "modes". Time to mention that Moen Monticello. That faucet was offered with porcelain lever handles originally, so the cartridge had a coupling on top that was designed to break away. Unfortunately, they broke a bit too easily and I had many callbacks replacing them. Moen did provide replacement parts for free, but I had to pay for the labor. Not a big deal if you can do it yourself, but if you have to call a plumber just once you've effectively doubled the cost of that faucet.
And that brings us to Delta- and why I decided to "butt into" this thread. While it's true that most plumbers love Delta, ask yourself if that's a good thing for YOU, the consumer! Why do the plumbers love Delta?
a) Faucets are cheap and common enough to be worthwhile stocking a few.
b) Replacement parts are cheap and already on the truck if not in toolbox.
c) Plumber makes more money from you for his effort if he doesn't have to go get parts (since he already has them).
He's going to charge you his $150 or whatever for the service call regardless, and it's easy to change a Delta cartridge- it takes me about two minutes flat, and most of that is getting the little setscrew out of the arm.
Now, let's do the actual math, assuming you paid actually $600 for your antiqued copper, was it? California faucet vs. $200 for a big-box cheapie. Chances are that finish in the latter is clear polymer powdercoat over a copper plated zinc base (lifespan roughtly five years befrore it starts blistering) and let's assume the much better California only has a lifespan of 15 years. Also, we'll assume the compression stops or nylon stops in the cheapie faucet never fail within it's lifespan. So, just on finish, and adding in the labor costs, over 15 years:
California: 600 + 150 install /15 years = $50 annual cost
Cheapie: 200 + 150 install + 200 + 150 replacement (5yr) + 200 + 150 replacement (10yr) = $70 annual cost FOR AN INFERIOR FAUCET!!!
In other words, you just paid 40% more for a faucet that doesn't look or feel as good as the better quality product.
I have been a renovator for 20 years, had an office in a plumbing showroom and sold plumbing fixtures for 8 years, and owned my company for 12 years. I specialize in bath remodeling, and the MOST COMMON mistake I see my customers make is to buy a similar looking, inferior quality product. If you are doing a bath in your basement, maybe a Price-Pfister is right for you. But if you are building a $30K bathroom and pick a Delta Monitor because your plumber recommended it, you are not budgeting adequately for your fixtures. And even for a middle-to-low end bathroom, cheaper initially does not always mean cheaper in the long run, as demonstrated above.
So, your plumber may recommend Delta for your kitchen sink faucet, but you may well find he owns a Hansa. If you aren't interested in learning about the types of faucets and the myriad of manufacturing types and finishes that determine the final price, find somebody you trust that sells a variety of products to assist you. Contrary to the overtone of some of the above threads, your interior designer was probably NOT ripping you off, but providing you valuable insight as to how you could get close to the $$$(Dornbracht) style and quality for a $$(California) price. Oh, and I'd say I'm impartial except I ran across this thread while ordering Californias- for MYSELF.
Note that some faucets use other valves as someone noted above, for example Harrington is built on Grohe Valves and Sheryl Wagner is famously (or rather infamously) built on Chicago compression stops. If you know this you can order replacement parts in the future from the valve manufacturer, otherwise order a spare cartridge "just in case"- it'll save you headache later in the event that one leaks.
But make no mistake about it, a cheap faucet doesn't save you money in the long run unless you are selling your house. Quality of the Californias is very good, exceptional when you account for the price. Nobody above mentioned this, I assume from their comments that they don't have experience with this particular brand. By their argument, everyone should buy a Hyundai and then go out to dinner with the money they saved over (insert brand of your car here if you don't have a Hyundai). This might work for some people, but if you consider the extended cost of ownership or you have an eye for quality or an appreciation for the tactile feel of a good lavatory faucet, this might not be the best plan for you.
Thanks for the suggestion. 
