Yep, and you need a 30-100 MB app for pretty much every little task you do. A good OS, built the right way, provides a strong set of basic tools that can be used together to do almost anything the user wants. Personally, I *do* want a real OS on a tablet - because there are just way too many real-world tasks that tablets either can't do at all or can only do with ridiculous levels of complexity and frustration. Real filesystems are just the beginning. FWIW, I'd rank the usability of tablet OSes for real-world use as first, Full Windows, then WinRT closely followed by IOS, with Android bringing up the rear. If there were a Chrome tablet (and WHY ISN"T THERE?), it would likely fall between the two Windows versions, and Ubuntu could well grab the lead if they can find any good hardware to optimize for...
Mark Shuttleworth and the rest of the Ubuntu guys get this, and that's why they're plowing ahead no matter the naysayers. Also, "full-fat" doesn't necessarily mean actually fat - IIRC, the first Unix System 7 CAD workstation I used had 4 MB of RAM, a huge 40 MB hard disk, and a stunning 1 MIP 68K processor with an incredible 1280x1024 display. Today's mobile processors have compute power only found in supercomputers not many years ago. Look at Puppy to see how slim you can make a "full-fat" Linux OS, even with a modern kernel and apps...
BTW, no OS exists in today's tablet/GUI world to let you easily snap together your own tools from a rich set of components - that requires GUI integration of the stream/operator paradigm as implemented in UNIX (but with different syntax and semantics making the gozintas and gozouttas intuitive), transparently merged with the browser and able to leverage not only local, but also remote web assets and applications. Add touch and non-touch dynamic gestural interfaces, and you've really got something...