Mate, the difference is hardly noticable, however from a principle thing, you were informed incorrectly of the spec of the car, now how you take that up with him, is upto you.
What i did notice though on alot of ads when I was looking and even up till today that the majority of garages, that dont really know much about the car, will always advertise it as a 225bhp, even if it isnt, as thats what they think appeals.
Guess its just a case of checking, did you do any checks/research when you were buying the car, as this could obviously have highlighted the issue before purchase.
Let us know how you get on with this......