So far from what I've seen I wouldn't say that XIII-2 is somehow "inferior" to XIII in quality.

Developing a major title in 2 years is by no means even that impressive (if its not an MMO). SE has taken way too long to get games out this gen, and so have Japanese devs as a whole. Even three years is starting to be a drag in this day and age, and you can hardly see it in the content or quality of the end product.

As long as the games don't start being rehashes of the same old systems (like FFVII-IX or AC) then I can not see the problem. Are you seriously saying that XIII-2 is coming "too soon" after XIII, or that Versus by 2013 will be "too soon" after XIII-2?