Jolly is right.... The Engliish often use '-t' instead of '-ed' - burnt, spoilt, spelt and so on. The rules are somewhat fluid, and at least as far as the English are concerned, common usage of a word / term / structure in language are enough to legitimise use.

Weirder ones are why the rubber things around your car wheels would be 'tires' in the US, and 'tyres' in the UK... I guess things like that were/are about American people laying some claim to the language by bending it a little.

Some people take this stuff very seriously. The militant types can usually be found moaning about correct use of the apostophe....