That's one of my biggest gripes about the iPhone (and the Kindle and others). The provider can retroactively disable/delete items you've purchased and use at any time.
Apple decides they want only Safari on "their" device line, they can not only stop selling the alternatives, but can disable it on any device that connects to the network & syncs up.
This happened on the Kindle too, when they ironically pulled several Wells titles off people's devices, including 1984.
With the N900, I can make a snapshot of just about anything and restore it back, without fear of Nokia deciding what is and isn't allowed on my device.