I trust the oil life monitor. Engineers are engineers for a reason, and they know about engine management, which is why I trust the oil life monitor. However, as to whether the car knows the intervals between starts and heat cycles is only info the engineers would be certain of. I would assume W4M knows a bit about this since he has extensive programming knowledge. Maybe he'll chime in on the matter.
An interesting note is that the monthly check that is made by OnStar will stop showing oil life percentage left after a year (just puts -- where the percentage usually is). It then starts recommending that the oil be changed. It continues to do this until the oil life monitor is reset, regardless of the actual oil life left.