I think the biggest thing about healer wipes... are the DDs that let it happen. The tank isn't some infinitely aggro-ing machine, sometimes a mob gets loose. If that mob goes for the healer it's the responsibility of the DDs to spam the every love out of that mob, grab aggro and drag it back to the tank. At least, that's what I do in those situations, and I like to think other DDs aren't so daft as to not do the same. The whole party may set the pace of a run but the healer is the lynch pin of the entire thing and needs to be protected at all costs.