If you look at their position, they sit right above the rocker cover. Realistically, this would be one of the hottest parts of teh engine bay (except for above the exhaust manifold but, if there was a vent there, the hot exhausted air would go straight into the cheese grater and heat the I/C core up even more !).
Having siad that though, the standard holes don't seem to be of much use either. That's why (as soon as I get off my ass) I'm going to open them up and make as much use of them as possible.
Paul