> Well, if you read the link, , they're called plutonians or something.
Plutons. But that's a different thing. It's to name only objects that are near-like planets. It's part of this whole silly proposal.
> Doesn't anything with any kind of gravity have an atmosphere?
It depends on several factors. Definitely mass is the major one. But temperature plays a big role. Too much cold and the atmosphere freezes to the ground. Too much heat and it evaporates into space. "Too much" here being obviously a relative term depending on the type of atmosphere. Other factors that can take atmosphere away from a body are distance to the star and the type of star (a red giant will definitely consume the atmosphere of many of its planets).