As a sponsor who has done 100% Revshare promos before, if you are doing a limited-time promotion you often expect to lose a little on it. Consider it part of your marketing budget, the idea being to attract new traffic to your program and hope some of it remains when the promo ends.
I think it is wrong for any program to charge the affiliate processing fees. I know one program who I like except for the fact their 60% is actually ends up as 53-54%. The program should swallow the fees and adjust their payouts accordingly IMO
For those programs who do offer a true 100% Revshare that's not a promotion, you have to think they are doing one of two things: making money from upsells, in which case more power to them if it means they can pay you more money out, or shaving you which with most programs is easily detected if you put a little effort into testing them.