Not all touchpads are near where your thumbs would be. On my DiNovo Edge it's over on the right hand side of the keyboard, and on my Macbook Pro it's in the center, but it's far down enough that I have to try to hit it with my thumbs (which is handy for doing mouse movements when you don't to move your hands from typing position.) If I'm really sloppy with my wrist angle, I will hit it with my palm, but there are usually driver settings you can tweak to filter out inadvertent taps, or taps that occur while you're also typing, so in practice it's never been a problem.

Not for everyone, though.