Actually, it was done a few times over the years, but nobody paid attention because 1) the technology or price wasn't quite ripe, 2) it wasn't let out of R&D, and/or 3) it wasn't done by someone with high publicity.
One of the best examples I can think of offhand, was the Norwegian
Freepad back in 2000. Like the later iPad, its UI was created specifically to be touch friendly, and designed as they put it, so that it would be "
so easy to use, that your grandmother can use it," Sound familiar? Its specs read just like an iPad would've back then... including having a dedicated app store.
Similar touch friendliness was tried with phones. One example is the 2003 MyOrigo touch phone with swipe between menu pages and integrated 3D orientation sensor:
Ditto for other multi-touch, pinch zoom, etc devices that came before the iPhone: most people never knew about them, but it doesn't meant they didn't exist. Lots of technology isn't known by the mass consumer until they can buy it.