Pine and Spruce Streets weren't always paved, horses were the main form of transportation, not hatchbacks, and if you lived in Philadelphia in the olden (sp?) days, wiping your feet (or your boots, more commonly, I'm sure) was of utmost importance. And why wouldn't you if you had a sweet boot scraper right outside your door?
Many of these muddy relics still stand strong on the streets of Philadelphia, serving no purpose except, well, to give us something to talk/blog/joke about.
So, I love Philadelphia thanks to relics of history for history's sake. Wipe your boots!