This also started happening to me recently, and i also suspected it was due to oil. I changed my oil to a 5-30w (was a 10-40) and it happens less, though it does still happen once in a while. I'm wondering if it isn't the oil pump. My car has only done "61000" kms, but maybe it's time to do the 100k service and change the oil pump. Not sure if you can check the health of the oil pump either... the pressure seems to be fine, but like your experiencing, sometimes on startup it will want to stall and the revs drop right down.
It also sounds silly, but it doesn't seem to happen when i hold the key in the 'start' position a fraction of a second longer than i ordinarily would... does that indicate a tired motor?