Did you test this? On my iPhone (iOS 5.1.1), the above css snippet disabled automatic text size adjustment.

If you have an iPhone, look at my test pages to see for yourself:

http://jabakobob.net/2012/08/hntest/test.html (without snippet)

http://jabakobob.net/2012/08/hntest/test2.html (with snippet)

For me, the first page renders with a much more legible text size.