Are TWitter handles overseen by ICANN and IANA? Are they bound by any type of international agreement?
The problem in your example is that the people behind TPB work with the principle that any domain name might be taken away from them at any moment, unlike Mr. @music, who was naive enough to think he was immune to any takeover just because he called dibs on the name.
To go back: the problem with your analogy is that it's not about the land, it's about the house.
ThePirateBay didn't build their solution on the premise that they would have an irrevocable right to their domain name. If the land owner decided to take back the land (like they did, many times) TPB could simply take their things and move elsewhere (like they did, many times).
I don't think I ever saw someone from TPB saying "oh, they took our domain, it's so unfair!", instead what I hear them saying is "we are building magnet-links and a bunch of redundant proxies so that our service continues to exist even if we lose all the domains we have.
In case of domain registries there is a contract with clear terms.
In case of twitter handle or other free services there is no consideration on user's side so there is no binding contract, therefore the service could be revoked at any time.
