Some riders have this problem, but not all (I don't) so I think it must have to do with your build. I did ride in a Bates that was less comfortable than usual, but I can't say I was truly sore, however, a good friend of mine had a big problem with this. Hopefully the suggestions you've got will help! It does seem somewhat common.
For me it's my inner thighs if I ride in a Western saddle. I'm fine in a variety of English saddles, and even my Australian saddle, but Western saddles really jab my thighs so I probably need a more narrow twist. It was unpleasant enough that I won't ride in a Western saddle anymore.