Part of the problem is that GW and WoTC have reached critical mass - they cannot expand any more in their given market. They are both trying to expand the market itself (both have released statements saying their goal is to make their respective rulebooks something 'every home will have'), and both are investigating Computer games. In the mean time, they are raising prices in an attempt to have steady profits. However, considering reports that all the 'geek' industries (RPG's, Mini's, Sci/fi & fantasy books) are on a downturn it would look to be unlikely at best.
As a side note, someone (can't remember who now) made a rather disturbing point. The new D&D MMORPG is coming soonish. It is not unrealistic to suppose that if it takes off big it could swiftly surpass D&D itself in profit-making for WoTC. The question is if, at that point, WoTC will not start changing D&D to fit the MMORPG better. After all, it's sound business sense.