I couldn't imagine Firefox 2 users being anything but lazy, though. I think a lot of people have upgrading issues, anyway (A theme I had on Firefox 2 kept me from getting 3 until I uninstalled things).
Inconveniencing the user wouldn't do anything, anyway. We can shuttle them off in another direction and just forget about them, or we could do something, somehow, to make the companies themselves upgrade from IE6 (or, more specifically, upgrade from Win95 or whatever they're using).
On second thought, the people using those computer might have installed Firefox 2, if Firefox 3 has issues with really old computers like that. Maybe that's why you're getting so many of those.