Most other Angel, VC, and incubator programs run a "rolling admissions" process. That would seem to take some of the time pressure out of the equation, but "time" as a limiting factor sounds more like the residue of inadequate productivity or know-how, or a function of the processes and structures the YC founders have put in place.
In other businesses, for example, if the number of startups that could take part in the program and offer a possibility of profit/upside or what have you for the investment of time and $ the business would find a way to address at least a majority of the demand (or unmet need). If YC had been funded by YC I would suspect they would be encouraging themselves to expand in a way that continued to create a compelling experience and a reasonable expectation of profit. Perhaps they are, since they talk about taking on more startups each time. I was struck by this article by George Gedron on the critical need for entrepreneurial education in the real world in Inc. http://www.inc.com/magazine/20071001/guest-speaker-the-real-...
It seems that YC is one solution (and if they make a nickel while doing so, more power to them). But Gedron isn't limited by time (any more than any of us are) because he is building a scalable repeatable model targeted at undergraduate education. I am not trying to play devil's advocate, I see a need for a factor of 100 to 1,000 scale up in what YC is doing (defined more broadly as entrepreneurial education, not just aimed at web applications).