The biggest attraction (to me) for the M11A-1 is the anti-corrosion coating applied to the Mk25 and original P228 M11A-1 used by the military.
In truth that will likely never matter but I like having a gun (or 2) with that extra protection
I don't actually care it is a P229 with P228 labeled grips. I can't understand how that is at all relevant
A P229 is a great gun and while most of my pistols have rails I prefer a few to not have them.
I understand making a gun that has ties it to a real military sidearm even if it is a mimic version is just good marketing so why wouldn't Sig tap into this desire.
For someone like you who wants an M11-A1, an excellent gun in its own right, then you are right, the P228 grips don't mean anything.
For many, if not the majority of, hardcore SIG fans the P228 is considered the best standard production pistol that SIG has made and maybe even a grail gun, and they find the P228 grip marketing a little annoying and confusing, if not down right deceptive.
For the casual gun owner who has heard of SIG and read the glowing reviews of the P228 and the cult-like love for it by SIG fanatics, then the P228 grips might attract them to the M11-A1 kind of like Darkstar888 mentioned, thinking it is a P228.