I've been talking about this for a while now: eventually the TV to DVD market is going to implode on itself and backfire on the companies and studios that keep pumping the market full of crap.
Think about it: if people keep buying DVDs, when are they going to find time to watch “live” TV? Sure, there are collectors, but the average DVD buyer still only has 24 hours in the day. The one-time purchase of the DVD allows viewers to watch episodes without commericals, which is how the TV shows “made money” to be produced in the first place.
I would argue that part of the responsibility lies in the studios to produce new shows that don't suck and thus encourage viewers to turn elsewhere, but for every good (or even halfway decent) show that comes out, a box set will soon follow thus continuing the cycle.
I wonder why advertisers aren't crying bloody murder, because they are the ones being cut out of the picture. After all, since most series coming out are almost certain to eventually re-bow on DVD, some people (myself included) would rather just wait and see them all at once without commercial inturruption. Sure, you're still gettin' paid, but if the paradigm isn't changed, expect to see the advertisers that give you the money to broadcast the shows in the first place start to put their money elsewhere.
Besides, people like me usually wait for their friends to buy the sets anyway and just watch them at their place.
Studios, take heed. You don't need any more competition with the way that network ratings are now being divvied up in smaller pieces due to the rapid growth of cable audiences. Don't fight yourself.