I wouldn't say they're nothing alike. The gestures developed for MacOS and the trackpad are paradigms derived from iPhone touch screens - swipe, pinch, zoom, tap to click (if turned on). And for the Mac, cognitively, at least with the cursor, the trackpad surface maps intuitively into the area of interest on the screen.

I agree, typing on a trackpad "keyboard" would suck, but on a Mac w/ a built in keyboard, that's superfluous. And who actually enjoys typing on an iPad on-screen keyboard?