Bear in mind that Android and iOS already use, more or less, the tiling paradigm (at least as I use my tiling WM -- most of the time my apps are full-screen). And both Windows 8 and the new OS X 10.8-era full-screeny thing are moving in that direction, as well. So I don't think making distros go tiling by default is likely to cause any problems. (Frankly, Unity and GNOME 3 already go in the same direction.)
It's not imperative that we always slavishly follow the proprietary OSes' UI paradigms to attract users. Many times it's useful, but it's not a requirement.