I agree with Bobbler. In addition, I'd like to add that an equal marketshare among two or more competitors will also increase the load of multi-platform targeted software - which, thanks to their nature, will make even worse use of the hardware. How this benefits the consumer is beyond me, really. Also, as I already mentioned (which you ignored), unless any of the competitors make any effort to change the cycle process (starting new with every console generation), there's no reason to suggest it'll end up being a monopoly. If consumers and publishers support it even more, they'll likely increase their marketshare, sure, but they couldn't afford to waste time on milking the market for an extended period, since this would make it easy for new competitors to come up with a better product publishers would jump to. There are examples of when this happened in the past: Square jumping ship to Sony for various reasons, Sony taking over the console industry despite a very dominant Nintendo, PSP's entry as a new competitor into the handheld space where Nintendo didn't have any competition (*note: That didn't stop Nintendo from releasing newer hardware didn't it?).
Fact is; there is no monopoly and there won't be for some time unless one of the dominant player changes their strategy. There is competition and if the competition can't sell their product successfully (for example Microsoft in Japan), then they're obviously doing something wrong and that's hardly the fault of Sony nor are the consumers. If demand is there for that product, people will buy.
Another thing which you ignored is, that a too short cycle isn't to any benefit for the consumer either. The best software usually launches in the second half of a console's life because assets / libraries are around enabling software developers to recycle existing code and concentrate on other aspects that will enhance our gaming-experience. It also enables them to make more money (through lower costs) which will in turm give them the opportunity to invest into newer hardware / new assets / new libraries when the hardware shift occurs.