> Current interfaces are generally a lot more simpler than those ones though?

Unless and until you need to do something that isn't one of the three or four basic functions.

> Are you saying those elaborate 90s style window menus are somehow simpler than iPad interfaces?

A perfectly-designed window menu is going to be simpler than a perfectly-designed iPad interface. There's only so much you can really have access to in iPad/Android-land, and any functionality that can't be encompassed with tap/long-tap/tap-and-drag is going to require a drastic break from the ordinary functionality. With window-menus, since you're already using window-menus for lots of stuff, it's not as drastic a break from the routine.

Now, I was careful to say "perfectly-designed" for each, because around the edges it can absolutely be a bit of a pain (my favorite go-to example is finding a "preferences" menu, which in Windows software can be in any of File > Preferences, Edit > Preferences, Tools > Preferences, or Options > Preferences - among many other options; and sometimes there's even a separate "Settings" menu with different options buried somewhere else), but even so, more often than not, window-menus still win by virtue of flexibility.

Touch-screen interfaces today are anything but "perfectly designed". The most effective and most easily controlled UX action on a touch-screen is a swipe, so if complex interactions are a priority you should pick something like pie-menus throughout. The basic idea is that what takes multiple clicks on a mouse should ideally take only a single swipe motion (with confirmation for destructive actions) on a touchscreen.