For Master's admissions, are recommendations from academics preferred? In making an application to a Master's program, would I be wise to seek recommendations from academics, practitioners, or both in balance? Or would any credible letter meet the required threshold? Or does this not matter?

I can easily imagine that for PhD programs the balance would be tipped towards letters from academics.
Normally, you should prefer academics, but you want the people who can most honestly attest to your accomplishments and the likelihood of your future success. 

However, if the MS is focused on things outside the normal academic tracks, on, say, industrial practice, then a letter from a practitioner who also has the ability to fairly evaluate you would be fine. But for academic subjects or in a field that can lead to a doctorate now or later, academics would probably be better. 

But also note that you are appealing to an admissions committee that has a certain background and certain views. You want that appeal to be successful. Thus, if you expect that they all have an industrial focus, then someone (again, who knows your abilities) from that industry would be good. 

For doctoral level admissions, you are right. The balance tips more firmly toward academics, but exceptions occur even there.