tangor - 8:04 am on Aug 12, 2009 (gmt 0)

s it an obligation? As in, legally you have to buy them or else, you could lose the trademark in court for not protecting it?

Exactly! Failure to protect the trademark produces dilution of the mark. When enough dilution accumulates the trademark is lost in legal battle. Some famous trademarks lost: asprin, kleenex, scotch tape...

Trademarks are forever (as long as registrations are filed timely and properly). Copyrights are finite (though these days its near a hundred years).