The problem isn't the ability to mimic a two button mouse -- the problem is the ability to mimic a *three* button mouse. Standard Unix/Linux behaviour on a three button mouse is left mouse to select/click, middle mouse to paste, and right mouse to... well... whatever the right mouse does (context sensitive menus, I think). With a two button mouse, you can emulate the third button by pressing both buttons together -- much like the way you're emulating a two button mouse via a tap/press+button click.

I'm with Mark -- I want more buttons on the track-pad. If I had the right expertise, I'd start a company whose primary service is modding apple laptops to have multiple buttons.