5 miles an hour doesn't seem like much, but it can be an important factor in changing the way motorists, pedestrians, and cyclists interact with each other on the street. Lowering the speed limit to 30 mph or lower can make a big difference by reducing traffic accidents and providing pedestrians with a higher level of safety.
This is something that I have noticed living and commuting in Missoula. The streets that have a 25 mph speed limit are very safe for other types of road users. The vast majority of the time motorists will automatically stop for both pedestrians and cyclists (even though they are not supposed to with cyclists). On the major arteries of our town however, its a nightmare to get cars to stop, and crossing at a light becomes the only option. If a car did stop, it would most likely cause a traffic accident.
Even on the major arteries that I cross on my commute, as long as the speed limit is no higher than 30mph, the vast majority of cars will yield the right of way if they see you early on and have enough time to easily stop.
Can you imagine trying to get across traffic like this as a pedestrian? Hell no.