As it turns out, homeless people can't easily keep laptops on them and afford to hang out at Starbucks all day. Public libraries give them and other low income people opportunities to develop skills and education, and electronic resources to find a long-term career that can take them out of poverty.
If that is truly a massive trend (and it seems like it would be reasonably easy to measure), the current setup of libraries is not that conducive to employment preparation (mine still features books on Macromedia Flash and Office XP).
One can probably run it more efficiently as an Internet access room at a local community center, with access to printing/faxing/tutoring/resume building and other services.
And, just as you said, some zip codes will benefit from this setup more than others.
