No, ride whatever bars you want, with your hands in any position you want. It doesn't make you a cretin.
However, whenever I see someone riding on tops (and I mean from lycra clad roadie to mountain bikers), I can't help but think "rank amateur". It's the equivalent of people who drive cars with their hands at 10 and 2.
Cretinous? no.
Don't know how to ride properly? yes.
WTF? You don't know what you are talking about.