Having no knowledge of the founders at all, I would guess that some of the founders graduated from those universities and either worked at or know people who worked at those companies, and so they chose that list to start with because they were familiar with the range of quality they could expect of programmers from those places.
The second sentence in the quote outright tells you that they plan to expand this list. Presumably they could be convinced to advance their expansion schedule if there was a lot of demand from people not fitting their stated starter profile.
Basically, I think commenters here are making a big deal about something that's really just a temporary filter to reduce the volume of applicants until the company is ready to scale up. Maybe I'm being too trusting, but I didn't read anything sinister into it.