Or those rare cases where people upload it on a device they no longer own.
Since Twitpic's purpose was to post photos inline at Twitter, what proportion of their photos have they probably lost?
Given that they can't even cope with the idea of copying their pics off this old device, what are the odds that they can cope with the idea of downloading an archive from Twitpic?
I'm all in favor of companies letting you take your data out of any service you've used, on principle, but frankly, this scenario doesn't make a lot of sense.
Anyway, that's an extreme case, and web services are typically not set up to deal with extreme (in fact, totally hypothetical) cases.
I still haven't seen anybody put up a rational counter-argument. Does that mean nobody can?