Yes it has, just as Apple's business has changed, press coverage of Apple has changed, and Apple's ad campaigns have changed. News, rumors, speculation, questions, and discussions all reflect that mixture of Mac, iPod, and iPhone topics.
The composition of our membership has changed too. Once upon a time, nearly every MacRumors member was a Mac owner. Now there are a good number of forum members who own iPods and/or iPhones but haven't (yet

) gotten a Mac.
The nature of a forum system also changes simply by growth. Registration, thread, and post rates have all continued to accelerate, expanding the breadth of discussions but also making it harder to follow a specific topic. For example, if your interest is iMacs, you can follow the iMac forums but you'll probably have to exclude a number of other forums (see
JohnNotBeatle's post above) before the Forum Spy and New Posts displays will be useful to you.