I'm sure that this question has been asked before, but I will ask it again.
Why did WH make the 27 magazine catch different from the 28 magazine catch?

We all know that it is perfectly legal to put a 28 catch on a 27, so it could not have been a ruling by the ATF (it would seem.)
Maybe it it was a marketing trick

Does any one know the answer to this question? Or have opinions on why they did this?
Thanks,
Norm