Actually, 28% has always been the number other than when the Federal government screwed with it and caused today's economic mess.
If you walk into a bank today and apply for a conventional loan, the numbers are 28/36%. FHA loans are 29%/41%.
Back in the 1980's, the debt to income ratio for first time home buyers doing 5% down and PMI was 28% housing+taxes+insurance/33% total debt. You basically had to zero out any credit card debt and you couldn't have an expensive car loan.
With those criteria, default rates have always been quite low. After a decade of total insanity, we're right back to where we started.
If you want some links to support those numbers, here are the first two on Google:
http://www.bankrate.com/finance/mort...ou-buy--1.aspx
https://www.wellsfargo.com/credit_ce...nders_consider