I feel that the psychological effects of publishing revised and enhanced versions of books too early are manifold, although sometimes too subtle to be immediately recognized. Just look at WotC's Star Wars desaster. The buyers of the first version felt alienated in most cases; this has long term effects on product sales. The company might even get a bad reputation despite good sales figures of the revised version; people will get the impression that said company tends to publish unfinished product and uses early buyers as beta testers. Thus, the damage will be made to sales figures of future product, not necessarily to the revised version of the first book.
Regarding WotC and their numerous changes to 3.0 after only 3 years, I first thought, it would not bother me. I got the revised edition quite cheap and thought it was okay. In the meanwhile I recognized that this move had lasting effects on my general D&D and d20 buying habits. With an expected half-life of about 10 years, I used to buy quite a lot of stuff. Seeing this half-life of unaltered utility reduced to only 3 years, I feel different now when I think about spending some $$ on D&D/d20 products.