I don't think they are being artificially inflated, I think they are in demand.
I personally have never seen, or met anyone playing 4th edition (or even buy any 4th material). It's all 3.5 or Pathfinder here. If the demand is still there for 3.5, why not make a profit on it.
It's a combination of things.
If you're not WotC, then you have to get WotC's permission to distribute WotC's stuff (copyright laws).
If you are WotC, then anyone printing your old stuff is in direct competition with your new stuff (as it fills the same essential market). Anyone selling your stuff is using your research and marketing base to sell stuff to your potential clients, undercutting your profits.
If you are WotC, then there's an additional problem with other people selling your old products: The D&D trademark. Can't have it distributed by anyone else, as that would cause severe problems and complications of various natures (legal stuff).
So in order to legally print a 3.5 Player's Handbook (or Dungeon Master's Guide, or Monster Manual, or Spell Compendium, or ...), you must get permission from WotC. And WotC has two very, very good reasons to say "no". Essentially, you'd need to buy controlling interest in Wizards of the Coast, or come up with enough money to purchase the entire D&D franchise from them (and it's a profitable franchise, so they'd be really, really loathe to part with it) before you can print any WotC 3.5 books in a legal manner.
Or, you know, take a set of books to a place where copyright law doesn't apply (International law is really multinational treaty - there's places where it doesn't apply), copy them there, and try to sell them there... but good luck with that, as the only places that don't participate in copyright laws don't have noticeable markets.
will probally get the new 4th ed books for Darksun just to help convert for the setting for 3/3.5 as officially as i can.
