"Is there competition? Is someone else doing a tablet that you can't upgrade, has no keyboard for when your touchscreen breaks, can't take external USB devices without an adapter, doesn't have an SD card slot (again, without an adapter), restricts you to purchasing software from a single retail outlet, and which doesn't support multi-tasking?"
That'll be Archos you're thinking of, with the possible exception of the Archos 9 - it can multi-task. That said, the reviews have found it to be so dire just single-tasking that it sounds a bit pointless.
Can't upgrade it? No. There are a handfull of "tablet" machines on the market already, larger ones are based on existing laptop technology and the new smaller ones starting to appear are based around touch screen. I don't expect any of them to be easily upgradable, if they even can be.
Yes, if your touch screen breaks you're stuck, but then if your laptop/netbook keyboard breaks you're in the same boat (yes; you can plug in an external keyboard, but guess what? You can do that with the iPad too, or use a Bluetooth one).
Can't take external USB devices without an adaper? Erm, so what? My laptop can take a few but I hardly ever plug anything in. What vital piece of equipment do you think you'll need? I can see why you might want to use an external mouse/keyboard on a netbook, but you can use a wireless keyboard and with the touchscreen the mouse is likely to be pointless anyway.
Doesn't have an SD card slot. Again, so what? My current phone uses micro-SD (or mini, can't remember) so would need an adapter and my camera uses Compact Flash. Point is, even with a machine /with/ an SD card slot I still have to carry adapters and a card reader.
Yes, you can only get software from one place, but so far Apple have done a reasonable job. The app store compares rather well with offerings from Nokia, Google and MS (especially as they haven't bothered).
Multi-tasking. Not at the moment, but if the rumours are true it'll be along a little later in the year.