There is certainly truth to that, but it all depends on what you will be doing.
A mountain bike is obviously ideal off-road, but at the same time, the level of mountain bike, mostly related to suspension depends on how serious you are and terrain you are going to be riding.
If you are mostly going to be riding on the road, then you are better with something road specific or hybrid like.
Main reason I stress it is that I've got friends who have bought mountain bikes, with the prime intention of riding on them roads, but then also doing a bit of off-road. The reality is though, that they have never taken them off-road, so they are commuting on bikes that have front suspension and are better suited to off-road than what they are really being used for.
So really its making up your mind what you will be doing in terms of riding.