This all seems like "Much to do about Nothing".
US Airways is matching LUV fares, and that's a good thing. US Airways must be competitive. And the fact that they are trying to do some marketing with it is also good...
But, if US Airways does not extend this to other hubs, or even non-LCC markets from PHL, it will only be a matter of time until a LCC enters the market.
For example... PHL-MKE. No LCC, probably not part of GoFares. But I can see a scenario where AirTran adds the route, or Midwest becomes a low-fare carrier over time.
Until US Airways goes to a simplied system-wide low-fare model, they are simply inviting LCC's to each market, one market (usually the next highest price market) at a time.
By the way... a low-fare pricing model does not mean lowering the price on every seat... When AWA did it, they RAISED their lowest junk fares, revenue manage them so they are harder to get, while lowering their highest fares. The combination of these two items raised the average fare level. That is what US Airways needs to do... Not to necessarily be the lowest price guy every day all the time. Southwest is often not the lowest price carrier, especially 21-days or more in advance. Several times, I have tried to get a Southwest deal where Southwest was sold out at $99 each way, but the other carriers matched and had seats available at the $99 fare.