Gas would not be able to make it 'around' the primer. Only way gas escapes through the flash hole is if the primer blows out, which will indeed cause erosion over time. Very rare for factory ammo.
If anything, it would be the poor expansion of aluminum causes some gas to come back around the outside of the case walls and erode the slide, but this also seems very very unlikely.
Guess glock's steel just ain't what she used to be.
I reckon glock would probably blame it on lack of cleaning, somehow.