I'm actually less inclined to be in favor of this for IPS than I am for other SE sites. Here's why:
Other SE sites (let's use Stack Overflow as an example), deal with concrete, black/white answers.
They tend to either be correct or incorrect (with the exception of answers that accomplish the same thing but have differences in styling preferences/conventions).
IPS posts often illustrate situations where it is impossible for an answer to be 100% correct and perfect.
Even in our own lives (where we have all the details) our interpersonal solutions likely don't always go as planned (because the involved people are so variable).
Posts are much more personal here.
While they can be read and translated to apply to the lives/situations of other users, each answer should be focused on helping the individual posting.
If an IPS user takes the time to read all answers and take action on what the general public considers to be a crappy answer but it's what works for them, I think the answer deserves to be listed at the top of their post.
Other users reading the post can easily see what the answer is voted as and decide to read other advice (albeit with a lot of scrolling) before taking action. Honestly, getting a larger set of advice before immediately taking action is probably wise to do for anyone browsing these forums.
p.s. For what it's worth, I am coming from a place of having an answer with 170+ upvotes that got shutdown by a +3 answer. I still think OP decision is valuable to display as primary.
p.p.s. In the case of this specific example you are discussing, the answer used to be quite small and not that great, but the answer-er recently went back and expanded a lot more on it. It could very well be greater advice now and deserving of it's place at the top. (I haven't read it myself).