I have a 6x8 Intuos 3. When in SW, I use it with the mouse exclusively. I don't see this as a limitation of SW at all. It would be tantamount to saying that Windows is limited because you can't work effectively with the stylus. Which I find to be true. The stylus is horrible for things like double-clicking, RMB, and scrolling. Maybe I just need to spend more time getting used to it.
My opinion is that the stylus is a very specialized input device designed to capture the motions of a pencil or brush, something which SW almost never needs to do (Matt's example is the exception, and I'm not even 100% on that). If somebody want's to use a stylus as a crippled mouse, then I suppose features could be added to make up the difference. Instead of using the wheel to zoom, hold a hotkey and drag with the stylus. Use a different hotkey to substitute for mmb drag to rotate the view, and so on, for all the things a stylus can't currently do.
Now then, the nicer tablets (like my Intuos3) have special features to alleviate some of this. I can use touch strips on the side of the tablet to zoom in SW. They work about as well as the touch pad on a laptop computer.
I wonder what it is that this particular customer wanted to do with a tablet. My first exposure to a tablet was on AutoCAD, where there was a fully customizable menu system in a tablet overlay. This seems largely redundant, since the advent of menus in windowing apps.
There is one area where a stylus might exceed a mouse in SW (other than emulating brushes and such), and it has nothing to do with drawing smooth curves. My stylus has pretty good tilt sensitivity. If I could spear a component with my stylus, and use the tilt control to rotate it as well as simply dragging it, that would be pretty cool. The same goes for view rotation. If the other limitations of using a stylus were addressed, and this was added, my mouse might actually begin to collect some dust.
I still don't see this as a serious limitation of SW. I can do what I need to do, and efficiently. Maybe that's because my tablet has a fully functional mouse (5 buttons + scroll wheel). A lot of tablets don't. I think people with those tablets should plug in a mouse with more than 2 buttons.
Since I don't use the stylus as my primary input device, I could be missing something.