Sure, CBS "can" put naitonal sports on 1210. They also "can" put all barking dogs on 1210. You've got about the same odds of each one happening.
As for the 38 states (and Canada) thing, let's set aside AM's problems with interference from seemingly everything. How many people--not radio geeks here, just average people--really think "Sun's down...time to fire up the old transistor radio and listen to CBS Sports Radio on a marginally audible signal out of Philadelphia"? I know, some people have rose-colored memories of tuning in whatever out-of-market station(s) they enjoyed back in the day, but it's 2015 now. It doesn't happen in any meaningful way (except perhaps for some die-hard Phillies faithful, and they don't count in the ratings). Someone who wants something out of town is going to listen to the stream of their choice--modern technology. And that's why media buyers buy the markets where the station IS, where the listeners they can measure are. Even if you can pick up 1210 in Podunk, it is essentially meaningless.
Sports talk's future, at least near term, is just fine in Philadelphia. We've got two stations that get the audience that matters, and one zombie AM station running whatever national feed they have today.
1210 is doing fine for what it is. There are zero viable options that will do anything to suddenly elevate them into the upper echelon, and that's perfectly fine. It's one piece of an overall businsses that's contributing to the bottom line.