Precisely.

Now this is one important point that does need to be foot-noted on all of this: Weather OC, SR, Under-volt, and friends are going to save you battery life depends on your personal usage pattern. If you're listening to MP3s with it all day, OC is not going to help you much, where SR or UV may. If you're using it as a PS2 emulator, SR may not be as useful, though OC is probably required. If you're using it as a PDA with IM and e-mail checking, then OC may save a huge chunk where SR/UV may just be marginal.

Testing with just media playing is great, if that's your primary target. But lots of people use their N900 for lots of different tasks. Saying that OC isn't saving you much battery with your usage is fine. Saying that applies generically to everyone, with much different usage patterns is another thing entirely.