I don't care what the RPI says, no MVC team with 6 or 7 losses is going to get an at large bid, period. Creighton with 6 losses or WSU with 6 or 7 losses means that each was either swept by two teams and also lost to 2 other teams that are not in the top 1/3 of the league and/or if not swept by someone, then lost somewhere to at least 2 teams that are in the bottom 5 or 6 in the league.
Sure a .500 record in a BCS conference is often good enough to get in, but how many times has a non-BCS team had more then 3, maybe 4 league losses and gotten an at-large birth. I haven't done the research, but I bet there aren't many. The only exceptions I could fathom is if a non-BCS league ends up in the top 5 in RPI, which is not going to be the case for the MVC this year.