Ba humbug!
Don't get me wrong, C/C++ are great for the hard core of us, but I'm a web guy, and the idea of being able to get a TRUELY open source phone that I can create "apps" for right on the phone and completely modify every aspect of the user interface is enough of a selling point.
Besides, think of it from this perspective, kid gets a Mozilla OS device, kid hates small icons, kid learns CSS in 5-10 minutes and changes icon. Kid now modifies app and decides to make his own. Boom! A new app developer is born, sure it's HTML so what? Kid may now decide C++ is for him and move ahead to that.
Regardless of the dev side of the phone it's a easily customisable phone that is cheap.