Necro post here:
While that might be the case.
I believe it has more to do with the g37 grip frame being the same as the G22/17.
With the grip being smaller than a G21, the mags arfe designed to fit inside the smaller frame so the rd count would have to be reduced to accept the fatter caliber.
Have you tried to see how many rds of 45GAP your G22 mags will hold?
I recently picked up a G37 myself on a whim. At the price offered it was impossible to pass up as I could never be upside down when you considered the accessories, Heinie NS (2014) and the amount of factory ammo included.
My G37 had it's grip shortened to a G38(G19) and stippled , along with the trigger guard under cut.
Never thought I'd like (TRY) 45GAP or a stippled grip but this thing feels great and shoots like a dream.
http://www.ballistics101.com/45_gap.php
Found my new raining day burb gun...