This is a pet peeve for me too. The problem stems from people's belief that a single LEGO brick is a LEGO. This misconception is common in the US where I now live. These same people would look at you strangely if you talked about building a toy log cabin from Lincolns, as opposed to the correct term: Lincoln logs.
Use of LEGO to refer to a collection of LEGO bricks/pieces isn't strictly correct either although it hurts less to hear, - it is simply a contraction of the formal description "LEGO set", "LEGO pieces", or some such.