Is it? I'd love to see some real data on this. For sure, some have succeeded. But there have been a lot who've not done much (especially in academia, which seems to tolerate laziness if you're smart).
Outside of academia, one who I know pretty well (he actually went to IMO, not just MOP) was no-offered at two different hedge funds because of the "tallest nail" phenomenon. When people found out that he'd attended IMO, there was a certain glee with which his co-workers (at least, in one of those two firms) made sure that he failed. After that, he was pretty much unhireable.
Outside of academia, one who I know pretty well (he actually went to IMO, not just MOP) was no-offered at two different hedge funds because of the "tallest nail" phenomenon. When people found out that he'd attended IMO, there was a certain glee with which his co-workers (at least, in one of those two firms) made sure that he failed. After that, he was pretty much unhireable.