Delta to drop PHL-Boston flights

According to USA Today, citing the Airline Routes Update blog, Delta will stop flying between PHL and Boston after Aug. 17, leaving US Airways with the only nonstops on the route.

What does this mean for fares? My guess is, not much, since prices can't go a lot higher than they are now with just US and DL on the route. Perhaps Southwest, wihich starts service at BOS Logan this summer, will step in, or AirTran, a former competitor between the cities, will return.