Not sure if it's been said already, but input from non-M owners is not relevant in this thread - the temperature gauge in non-Ms is coolant, not oil!
Have you checked the Oil grade used in the last service? If it's too thick it could be affecting the heat of it? Essentially though provided it's good oil you shouldn't have any issues with 100C or so regularly, with 120-130 periodically during really hard use...
I realise quite a different thing, but I had a couple of old 306 GTi6's, both of which had oil gauges, which sat at 90 under normal driving, but climbed quickly up to 130C during hard driving - both engines were stong examples with no problems.
I shouldn't worry basically!