I don't agree with that completely. I keep my room 68 generally and have no problem with non-belly heat racks that are designed with adequate heat.
Heat rising, yes, but if the rack is engineered with each compartment enclosed and thus not allowing the heat to rise anywhere except out the front, it will heat just fine assuming there is enought heating surface. In fact, I think they do a much better job at creating ambient heat than belly heat does.
I have racks that use both and a correctly built rack using side or back heat is by far my choice. That said, a rack built that is not suitable for it is worthless, whereas, even a poorly built rack will work fine with belly heat.
just my 2 bits.
-d