Since about 1987, Federal regulations have restricted water use in various devices you can buy. Prior to that, they were pretty much unrestricted, so yes, if you have an old one, it probably has a larger inlet and, if you have an older supply valve, that may have a larger port to it as well.
Today, it's illegal to sell and in most places install a device that does not meet those guidelines. This applies to showerheads, vanity faucets, kitchen faucets, toilets, urinals, and most things.
On some devices, you can defeat that by just removing a restrictor, on many, you'd need to drill out the hole. You really shouldn't, but it's your house. Larger volume not only means more water used, but more energy used to heat it, and more water that needs to be run through the sewer system. Michigan may not have an issue with water, at least if you're near one of the lakes, but still...as a country, it matters.
FWIW, the pressure is identical, but the volume is down, probably considerably. It's a function of how many and how big the spray holes are as to the 'effective' pressure you feel just like a soda straw verses a fire hose, both being fed from the same supply...one will have LOTS more volume than the other.
Not all showerheads are created equal...there are actually some that work quite well and still abide by the restrictions.
