I just sold the TTR90 a couple hours ago, so I think I have around 10 now. And while that assertion may or may not be true, I would rather have 10 bikes than 2. I can think of at least 3-4 different reasons to have 3-4 different bikes available for use.
But here's the real question - WTF would I tinker with if I had 2 brand new bikes? I need to have a motorcycle in a state of disrepair in my life!
Trust me. With a kid riding and racing there will be plenty of things to tinker with.