Your analogys are off.
Mac OSX is more resource intensive than Mac OS9
HOWEVER, through out the 10 series, they continually work at improving resource usage and efficiency so that by the time you reach the end of the 10 series, it is as efficient as possible (and 9/10 more so than the first iteration of the series).
As I've said before, Windows 7 is what Vista should have been. Really it's just an update to Vista, however Microsoft doesn't generally do releases in the same fashion. They release patches, or an entirely new version, and not much in between. To that extent, since Windows 7 is building and improving upon Vista, my analogy above still stands.
Same with Firefox or Opera or Safari.
Firefox 3 uses WAYYY more resources than Firefox 2. HOWEVER, Firefox 3.0.1 improved upon 3.0.0, and 3.0.2 improved upon 3.0.1.
It's the same way here. IPB3 uses more resources than IPB 2 (as a blatant general statement - this largely depends upon the features you enable). However, 3.0.1 uses less resources than 3.0.0 did, and 3.0.2 improved greatly upon 3.0.1. It's probable that you will see improvements with 3.0.3 over 3.0.2. And this is what we've said all along in this topic. Over the lifetime of the 3 series, we will continuously improve the software so that it becomes as efficient as possible.
You have to use analogies that match up here. :)