The speed issue is definitely location-influenced. Here where I am in Monterey, I'll be mostly using a shared-path and will be peaking at around 15 mph simply because thats all that can be safely managed on the path. But on a weekday like today, heading out over to Seaside Home Depot, I can probably cut thru Cannery Row (thats a city street) and 25 will be no problem on that stretch. And worth mentioning... going downhill from near my home to sea level, I will be shooting down at 35 mph no problem, because steep downhill. Cyclists have been doing that forever on city streets and nobody freaks out over it.
In Fresno I have streets like you see on this link. 25-30 mph on a 15 mile commute makes a whole lot more sense than 15. For the same reason you don't want to drive at 15 mph all the time in a car. Simple convenience. This is the street I was thinking of when I mentioned hitting throttle to make a green light while it was still green.
