I don't consider that normal wear although I've seen it on Polaris pistons a few times. I don't know why the say that is OK.
I work on quite a few dirt bikes that never show wear like that even after seasons of use and abuse. I just pulled a piston from a CR250 with
A LOT of use that had not a hint of scoring and the coating was still intact after 3 seasons. That coating shouldn't be just for break in, it should be a last line of defense if something goes wrong. At least that is how I look at it.
The Polaris 800's even the earlier models seem to generate an excessive amount of heat around the exhaust port. By excessive I am trying to state that it seems like the piston and cylinder cannot dissipate it fast enough as that is where I always see the scuffing. Some contribute this too possibly a late opening exhaust valve. Hopefully someone else can chime in on this.
Take your precautions. Break in and warm up thoroughly. Run your scratchers. If you get the option, I also prefer to run engine ice rather than standard coolant or at least add some water wetter.