That said, the fact that you seem to think that cooking meals, gardening, woodworking, and appliance repair are also impossible indicates to me that you're not really railing about the iPad.
These are great days to tinker. Just a slightly different kind of tinkering, is all.
There is only 2 way such a thing is possible.
(1) By default, the iPad let you write, compile and run programs in it without requiring any external device (like a iMac with XCode). That would mean it is easy to distribute such programs without going through the App Store, just like with a plain old desktop computer. I don't believe it for a second.
(2) You had jailbroken it.
Therefore, it is safe to say that by default, the iPad is not programmable.
If you're not, jacobulous's ridiculous hypothetical scenario isn't worth treating seriously. And I treated it with all the lack of seriousness I believed it to deserve.
Now, imagine that devices like the iPad are the majority (like Windows is now). Plus, viruses and netbots are evil. Result: Trusted Computing everywhere.
This is of course the extreme, very unlikely scenario. However, this is so serious that I think it is worth to watch out, even knowing that the odds are almost nil.