I could see having a docking station that connects to external monitors, a proper keyboard and mouse, or any sort of standard peripheral, as well as an OS that's open enough to do any sort of general purpose computing, but the big sellers today are nothing like that.
My ~80 GBP 7" tablet has full HD HDMI out and support for USB keyboards and mice, as well as USB support for mass storage. Most low end Chinese tablets do... And most of the Allwinner A10 ones (the bulk of the low end Android tablet market) can run "full" Linux instead of Android and also tend to come already rooted and with unlocked bootloaders, taking care of the "open" part for the most part (only downside is lack of open source driver for the hardware acceleration on the Mali GPU).
The may not be the biggest sellers, but there are *dozens* of models of them, and they pretty much make up all of the low end of the tablet market.
It's certainly no speed daemon - about as fast as my 2 years old HTC Desire HD, other than for 3D where it knocks the pants of the HTC phone, but for that price it's pretty impressive. You can also get "Mini PC's" based on the same SoC that just does away with the screen / touch and are about as large as the Raspberry Pi - I plan on taping one to the back of my TV's.
