Utah win is in BYU's best interest. Since they are BYU's primary rival, and a local school so close to BYU, recruiting becomes an issue, and the worse Utah is, the more of a recruiting advantage BYU has, and the more good recruits BYU will get (or perhaps, the fewer recruits BYU will miss out on due to them picking Utah). This recruiting angle trumps the "we want them to do well since beating a 11-1 Utah looks better than beating a 0-12 Utah" perspective; it's ok to have some weak teams on your schedule and I'm more than happy to have Utah be one of those weak teams.
This weekend is different since a Utah win would directly benefit BYU; a Utah win helps BYU's current conference standings more than a Utah loss would benefit BYU's recruiting, in this one particular case.