I assume this is so that one could state one's personal opinions under the personal username, while keeping the business account "clean" or "neutral". It makes sense to me in that regard. Since the admins know who is who, real smurfing activity where the business account chimes i constantly to say how correct the personal account's comments are would be unlikely to be tolerated.
OK, I'll see you in there. I'll be whitecottonpanties.
However, if you don't have to be a sponsor to participate, why call it the "sponsor's only" forum?