I don't have a solid proof that this happens on SO regularly (but my experience tells me it's true); but I most certainly noticed this pattern on other SE sites.
On SFF (where I'm one of top users) there were definitely times when I noticed that my answer of OK quality got more upvotes than a competing - and much better - answer from a lower rep user. Many times the answers were posted in roughly same time, so that's as clean experiment as possible.
In some cases, I had to openly post a comment to question poster requesting that they accept a better answer and not mine (to their credit, 100% of time it happened, the poster changed their accept after my recommendation).
P.S. As far as SO, I am aware of some single examples, even if I can't prove a trend that I suspect is true:
Alan Kay got gazillion upvotes for basically posting an answer that amounted to "I don't remember".
Joel's Turtle LOGO question - leaving aside the quality and desirability of it, its votes were CLEALY super-inflated considering the low overall popularity of LOGO tag