The problem they have is if they scale the characters to the buildings, then the characters would tiny and be like 2 pixels tall. If they scaled the buildings to the characters, then the buildings would be fill-the-screen huge and it would take a hour to scroll across your Springfield. So it's obvious that the scaling mismatch between the characters and the buildings was an intentional decision so that we can see both the characters and the building on the screen at the same time, which seems like a reasonable compromise.
They've done a pretty good job keeping the scaling on the characters consistent with each other. Vehicles seem to mostly be on character scale, but the roads are building scale so the vehicles are as wide as the roads. They really need to be more consistent with the building scaling though. It's all over the place. :x
