Now you see why these are XXX pics, look at all that filth. Have you ever seen so much spooge deposited in one place? I imagine after re-applying thermal paste numerous times, the ventilation hole could become obstructed. I'm not sure of the effects of this, but, I don't think it's there for the release of epoxy gases as I've read before. Since there's small gaps in the seal anyway.
In the photo after this one the IHS was lapped, which is why it doesn't resemble what you may have. But if your thinking of removing your heatspreader, then you've most likely lapped your your by now anyway. Don't ask me why. I've heard the difference is marginal, I beleive it was more curiosity, which motivated me to do this.