to say that it's some sort of crazy coincidence that BYU (for no explicable reason) always underperforms against Utah every year comes across as a lame excuse.
What is the Utah / BYU head to head results in the past 11 matchups? It's very one sided. ALUF1990 made some very valid points that illustrate how maybe the success of Utah in the rivalry games is based on the types of players / athletes that each team has. For whatever reason the overall matchup in the BYU / Utah rivalry game has worked out quite nicely for the Utes because of the Utes strengths / weaknesses compared to BYU's strengths / weaknesses.
Based on current and recent player personnel, it just ends up being a good match up for the Utes.