I tend to agree with you - WN didn't "run US out of town" in various markets as much as US gave WN the rope to hang US with. From the west coast PSA system to the intra-Florida, US cut back and WN moved in.
So, US Airways should have stayed in cities that airways couldn't make work just so that Southwest airlines wouldn't come in?
How is Southwest exactley hanging US Airways? Why didn't American or United snap up the PSA operations?
Personally, I can't see any logical reason to give up LGA slots - expecially non-Express. As others have said, if US can't make money at LGA - the "downtown" airport at the biggest market in the country - things are really bad.
Hell, why doesn't US Airways just set up shop in Chicago or Miami. Them are 2 very large markets.