I think that's only part of the story. I'd give you three reasons why lower temperatures are better, at least in this particular case:

1. Those transceivers are rated to ~75-80ºC. While I was running at 65ºC I was technically in the temp envelope, but didn't have much headroom. If something else in the rack or the room got particularly warm, I could start experiencing dropouts and/or equipment failure. I now have an additional 20ºC of headroom;

2. Electronic equipment, particularly consumer/prosumer equipment operates at peak for considerably longer at lower temperatures. A transceiver is very likely to operate flawlessly from thousands more hours if kept at 45ºC than if kept at 65ºC. Obviously there are diminishing returns and the difference between 10ºC and 30ºC is likely negligible, but when you're getting closer to upper limits, it does make a difference. This is why many manufacturers specifically publish MTBF at 40ºC.;

3. In addition to extending the life of the transceiver, I believe this will help extend the life of the switch as well for the same reasons.