Yes, it's a terrible excuse, and it's concerning that they think it's a good one. I highly doubt that they make a habit of fielding requests from plugin authors to nuke outdated reviews: you simply can't scale the verification that would require to do honestly. If they don't offer this as an option to others then this move is wrong both for the reasons you give and because they're claiming a privilege in their app store that they won't afford to their competition.