Yes, I like that musing is upvoting even the old question. It is a fact that trees laden with fruits attract more birds. Same is the case with human nature, people find the platform more interesting if they offer you decent reward all the time. The more the reward is the better will be the people participation and better will be the quality. Quality never comes cheap. The reward system will attract many talented people to come on this platform which will help to bring this community to the top of question answer session.
What you have to understand is that musing is a business. Musing makes their money from curating on questions and answers.
By voting on answers to questions that are an hour old or 6 months old makes no difference to them. This is all about generating rewards and it is as simple as that. Every question is live as such and can be answered no matter how old they are. Musing will curate all answers if they are good enough as it is in their best interest to create an income.
It is a good development and a right thing to do,a good answer is a good answer no matter the hour and days it was posted....musing always upvote good questions and answers especially answers that meets the curation guidelines...so a good answer will get upvoted by the curators even if the question was answered some few days ago....
Aside from the fact, what cryptoandcoffee mentioned, musing is curating only those answers to old questions, which cover a unique or different angle of explanation to those questions, and no matter what ... this door is gonna be opened, forever.