This is pretty much true, where there is no assignment or ownership agreement (written or, at times, implied) in place. Each inventor has rights to the patent and can do whatever they want with those rights. i.e. say we have Inventors A & B. Inventor A can license his rights to the patent without Inventor B's approval. Inventor B however still, also, maintains rights to the patent.
I am almost sure that is how it works. If I am wrong, I am not very wrong. Its almost besides the point though, anyway...if you are ever in a situation where this worries you, just make sure there is a written partnership/ownership agreement in place or what not.- Bill