I sure hope there's a way to disable the touchscreen. My ThinkPad has one, and I hate it. I never want to touch the screen on purpose, so its only function is to unexpectedly move my cursor when my sleeve or something brushes too close.
I have Chromebook with touchscreen. It's great to mix trackpad and touchscreen. But after heavy use display became dirty because of human fat that remain on screen. I didn't notice similar things in iPhone/iPad however.
I suspect it's that phone and iPad screens do get dirty that way, but they're very easy to regularly wipe clean compared to a laptop screen, to the extent that it's not as noticeable that we're doing it.