Freestyle on fixed - I don't get it

People says the same with BMX, the same with MTB, the same with Cyclocross...

admittedy a track specific frame doing trick is quite unheard of, but the fixed wheel ablitiy make for interesting trick that BMX usually can't do with freewheel.

Wouldn't be impossible to put a fixed hub onto a BMX though would it? (although would make for some interesting riding without ability to sit at required height!)

Not sure how people could say the same about BMX or MTBs as they were designed for the purpose they are used for weren't they?