What I've always read has been to start with spiro, which does feminize to some degree, see how the body responds, and then add estrogen, gradually working up to what will be the daily dosage. The reason that spiro is used is to allow lower doses of the estrogen, estrogen being the main reason for caution due to possible serious side effects such as blood clots.
Progesterone is something that not all doctors believe in, and apparently it sometimes helps a lot, sometimes it does nothing. More so than most things, "your mileage may vary!" Some doctors feel that it creates an undesireable increase in the risk of side effects. Some doctors introduce it in the second year of HRT. Since there is no one standard that all doctors will follow, and since we're all medically different, the doctor has to be trusted to make the appropriate decisions, with all HRT being individually tailored to each transitioner.
You, of course, have the right to ask the doctor why he doesn't use something. I would be more concerned with the safety factor than anything else.