People naturally want to talk about whatever is on their minds, and that tends to depend on what they think is coming up next from Apple. The balance of Mac/iPod/iPhone discussions changes over time as it follows people's interests. (Hmmm.... a good idea for a graph!)
Then again, maybe we need more of those threads by people who accidentally ran over their iPhone with a tractor, and want to know if they should return it and pretend it was broken all along. 😛 🙄