Except arbitrary URL shortening services are far more likely to shutdown than Wikipedia, Google, or Twitter itself. It's another level of indirection through another party which provides a service in a fast-changing, simple market.
Are all the URLs in your tweets going to be broken in 2 years? More likely than a Wikipedia or Google URL.
so are the twitter image hosts. or arbitrary S3 file hosts. or a wordpress mu blog network. or any number of other smaller alternatives for services that we deem useful.
i suppose the root of my problem with this line of thought is that it basically is saying that if you want to start a value-added service, go big or go home. no room for little guys, because if you fail you might somehow be destroying some of the fabric of the web.
i find this disagreeable. seems not very hacker-like.
Are all the URLs in your tweets going to be broken in 2 years? More likely than a Wikipedia or Google URL.