The article is correct in noting that there is a huge tech community in the chicago area. Some of it is rather unique in the financial sector--trading, options, financial (more so than new york).
But as a distant observer to YC, isn't a key factor in YC's success the culture of the surrounding community (as indicated by the move from Boston, which is certainly more high-tech than Chicago to the valley) and the particular knowledge that YC has in doing this sort of thing?
And from what I have read of Jason's posts, he doesn't seem to think that building a company to be acquired is what he would recommend (in particular, his post regarding the selling of mint to quicken). I would think that would be part of what a YC-like outfit would need to have in its bag of tricks.
And, from a distance, there just seems to be this startup fever in the valley, not something that is really evident here in the chicago area.