I'm thinking about it more of being a miner problem. The only other reason for a miner to drop CPM is for an unstable OC. In Nvidias case, the power % drops and the clock speed goes till something like 575Mhz. So it probably should be both, however, I can't be too sure about people running linux.
I'm only mining on Nvidia atm. My miner never crashes or drops CPM as I've been able to find stable OC's, and I mine 24/7, it's the fourth day since the last time I gave the PC some rest (due to installing a card) and I just crossed 10 PTS in that time. The only other time it chills is when ypool goes down, like it did quite a bit yesterday.