Gravitons

Either I've got the wrong end of the stick, but if it's particles that mediate the interactions between everything at the quantum level, and nothing escapes from a black hole - except gravity - no radiation, no light, no other particles..... (with some odd exceptions) then obviously gravitons have a special dispensation, OR gravity is not mediated by a particle.

Since gravity also is defined as the curvature of spacetime, I doubt that there is actually a particle involved, virtual or otherwise. As a star collapses, it's density climbs beyond the schwarzchild horizon, and the gravity well gets extreme enough that nothing escapes (almost), meaning that it becomes a black hole. What does this mean? Does this mean that as the gravity gradient gets steeper that more gravitons are emitted (how? from where? its all the same stuff, just in a smaller space), or the nature of the gravitons changes and they get more....umm... concentrated? I don't think so.

The simplest argument is that there is no such particle, which begs the question about some of the other particles. I know the ether theory is obsolete, but if spacetime is bending in the presence of mass, then obviously spacetime has as valid an existence as some virtual particle, no?

enlighten me.