Other folks have pointed out the biggest thing that will prevent the major chain booksellers from caring about the transition to 4e - returnability. They're going to be able to return unsold books to the distributor, who will turn around and sell them to places that deal in "remaindered" books - some of these will show up on discount tables at Borders, B&N, etc. Others will show up at warehouse stores like Half-Price Books. This goes on all the time right now anyway (a huge shipment of remaindered Dungeon Masters Guide II showed up at all the Half Price Books in town just a couple months ago, for example), so I doubt that the retail booksellers will even notice when their small selection of RPGs undergoes a shift between editions (they didn't seem to notice much 8 years ago when it happened from 2e-3e, for example).
I do want to mention this, though:
Calico_Jack73 said:
What about the FLGS? Their survival DEPENDS that the books that they purchase from the publisher not sit on the shelves and collect dust. I love my FLGS but as I said before I can't see spending my money on an obsolete system.
Yup, FLGS's are going to be in for a bit of a rough ride I suspect. The fact that Wizards is going to be selling some "edition proof" material as 3e rides off into the sunset may help somewhat, but if they have a backstock of 3e PHBs, DMGs and MMs, this may hurt - those are items that are supposed to be saleable year-round, and we're entering a time where for the next 9 months very few people are probably going to be buying them.
The 2e-3e transition isn't the best model for determining the impact of this either - TSR had been bankrupt and bought out by Wizards, very little 2e stuff had been coming down the pike for a while anyway, and the money stream for a lot of FLGSs was collectable card games. It might be more like the 3e-3.5e transition, which I've heard hurt but was followed by a sizable sales bump when 3.5e finally came out. I'm hoping its the latter - I like to see money go to the FLGSs whenever possible.