I was replacing the batteries on my Magic Trackpad today and noticed something interesting: the two nub-like gray circles on the bottom are what enables the clicking:
To enable the ultra-thin design, Apple integrated the clicking mechanism into the base rather than making it a part of the trackpad (what I assume to be the traditional approach). My curiosity led me to attempt to click the trackpad while I held it in my hand but nothing moved. Only when I placed it on my desk did I realize the gray nubs were responsible for clicking.
Ever since Apple redesigned its trackpads to be larger and button-less, I have always appreciated their capability and elegant design. I’m not sure if MacBooks utilize the same structure, but I find this design very interesting and absolutely brilliant. It’s small innovations like this that draw me to Apple- I hope they never lose this attention to detail.