I suspect it has more to do with applications for the newest class being due soon.

When pg gave a talk while I was at MIT, it was in early October (of 2006 - yikes I'm old), about 2 weeks before apps were due (I didn't get in.)

Apps for this season are due six weeks from now...so I'm guessing the purpose is still to drum up applications, and they're just more on top of their game than they were six years ago.

That said, no one is going to not hand their resume to Google because they spoke to Y Combinator that same week - if anything, it's sort of poor timing, because they're now competing against the companies for attention (who are somewhat restricted as to when they can come to MIT.)