As has been pointed out many times, 23C tires will give you a different gear inch than a 20C or 25C or whatever tire. And I'm sure even in San Diego people are riding with different tire widths. Not to mention I have some really short friends who ride 650C wheels.

But even ignoring the usefulness of gear inches with respect to different wheel sizes, it is still useful for comparison. To give you an example I was recently in a roller race. There is a UCI gear limit to how large a gear you can use while roller racing. That limit is 7.69 development meters (the European equivalent to gear inches). Since you seem to be suggesting that gear inches (and by congruence, development meters) are somewhat pointless, why did the UCI specify the gear limit in development meters instead of gear ratios? Well the problem is that there are dozens of combinations of gear ratios and tire widths that will get you to the limit. To list them would be a lot harder and more confusing that simply saying, "No gear over 7.69 development meters." and let the riders do the calculations themselves (actually the officials mark off 7.69 meters on the floor and roll out your bike).

To give you an example, the following gear ratios and tire sizes will give you 7.69 (or at least, as close as possible) development meters:

for 700x23C tires:
53x15, 51x14, 47x13, 39x11
for 700x20C tires:
48x13, 53x14