http://www.post-gazette.com/pg/07055/764655-28.stm
Apparently, convenience stores cannot sell alcohol because the law allowing corner bars to sell to the public specifically states that purchasers be allowed to drink on the selling premisis. Thus, the convenience store would have to first provide a spot within the store for beer-buyers to cosume their purchase.

My first thought is that I'm looking forward to moving to Philly (only 6 more months!) so I can easily drive to other states to buy alcohol!