There is often a certain amount of subtle pressure from instructors to train in a C-172, rather than the lowly C-152. I.e., the novice comes in and says he wants flying lessons and the instructor signs him up for the 172, and the option of training in the 150/152 is not even discussed. If the new student checks the rental rates and does enquire about the 150/152, the instructor says "you wouldn't want to fly that, it is underpowered / too small / not as stable".
I am not suggesting that instructors are doing anything underhanded, just that most of them would prefer to have 172 time in their own logbooks and the student should take a somewhat jaundiced view of any efforts to steer him or her away from the 150/152.
Personally I did my PPL exclusively in 152s and then switched to the 172 for my night rating (I am 6'2", 180 lbs). I agree that the 172 is a more comfortable tourer and better for instrument work, but the 'planes are so much alike that I think most primary students are well enough served by the 150/152 and should save their money, which can be put towards additional lessons or a nice ENC headset or whatever.
If you can fly one, you can fly the other with only a minimal amount of conversion, i.e. a review of the POH and perhaps a one hour checkride.