I don't think that's true. In my 6th gen as well as my 7th gen, the heat would/will always wait until the engine is a bit warmed up before coming on .. The other thing I noticed (with the 7th gen, not the 6th), is that before the engine is completely warmed up, it will blow most of the air full blast out of the defrost vents .. then once it gets really warmed up, it switches to the floor vents .. Just an interesting tidbit.

--Brian