There's no goddamn reason for any non-system software to be frozen ever
What about, I don't know, developers who release early and often without good test coverage? If you're putting your seal of approval on a bunch of software, you probably want to make sure that it works. This cannot be done instantaneously.
That doesn't mean you should be shipping the version of Firefox released when you last did a freeze, whether that's 6 months or 3 years ago. Even worse, with the way the freeze cycle is done in practice, they need to stop all updates even for bleeding edge users for several months (Ubuntu) or 6-18 months (Debian).
In a rolling release system you don't have to have a single imprimatur of package approval. At minimum everyone implements it with at least 'stable', 'new', and 'fucked' markers for packages, and you can go way further with multiple repos and overlay semantics.
testing is the only one of those that's remotely usable, and it gets frozen as soon as they start thinking about releasing -- etch was frozen for five months, lenny for seven. Sid / unstable is generally frozen whenever testing is, is still really laggardly normally, and is constantly broken anyway. I've never gotten anything useful done with Experimental.
At least volatile has been around for a few years, so people aren't fucked on tzdata and such because of bullshit policy, though I think it's still off by default.
