RedHat and Debian aren't a mere "few distributions", they're the two major distributions that everything else (except niche distros like Gentoo) is based on. The fact that Qt 4.7 is binary compatible with 4.6 (but NOT vice-versa) is yet even more reason developers should target 4.6, not 4.7. Qt 4.6 apps will run anywhere (including Maemo), but Qt 4.7 apps will only run on niche future operating systems for the next 3 years. So, if someone is developing a complex app targetting release 3 years from now, Qt 4.7 makes good sense, and they don't care about Maemo. But if they want widespread use before then, Qt 4.6 is the way.