Sooner or later all 3 will make another console, but: Nintendo is in a strong position, so, it can decide its own release strategy undergoing very small influence and listening almost exclusively to public; Sony saw that releasing first didn't save MS, but also that previous leadership didn't save them, so they'll try to devise a good strategy and also to avoid the excessive cost that plagued PS3 for its first 18 months and forced it to have a launch price too high; MS still hasn't grasped fully the unwritten laws of this market, so either they'll try to understand more before deciding anything or they'll rush next launch too trying again to gain an advantage on Sony and Nintendo, but this could be fatal to XBox 720, as Sony put enough stuff into PS3 to make it a longlasting seller and will be able to ignore MS' moves and keep on selling PS3 till its natural time for changeover, while Nintendo choosed to avoid competing on pure performance field, so it will be able to continue undisturbed its strategy.
About others entering the market: as there will be one market leader, with more market share than the others, there will be room for only two other players with more than 25% share (the first threshold indicated in some studies on game theory applied to economics, 40-41% being the threshold for leaders and 70-72% the one to become a monopolist, leaving place for at most only another player with real influence, but no hope to become leader, unless the market starts growing strongly towards unexpected directions), so only three players, leader included, will really be influent, irrespective of how many competitors ther will be in all. And an excessive number of competitors could fragment excessively the market with damaging consequences for all, in this case the best sellers could remain the actual generation, just like XP (for different reasons) is doing to Vista despite every MS' effort.
Stwike him, Centuwion. Stwike him vewy wuffly! (Pontius Pilate, "Life of Brian")
A fart without stink is like a sky without stars.
TGS, Third Grade Shooter: brand new genre invented by Kevin Butler exclusively for Natal WiiToo Kinect. PEW! PEW-PEW-PEW!

