Scrubs does it too.
I personally think the original reasoning is flawed to some extent because Television isn't just a visual medium, it's both vision and sound and showing a persons thoughts is really hard to do, which is why movie versions of books are never the same, because you don't get the "internalizing" (as it's called these days). Voice-overs allow for more much more information to be presented in a single scene than just image alone.
I think the voice overs worked well to help "show" us the thought process of MacGyver piecing together a MacGyverism (which is something RDA often commented on in
his interviews) but also to give extra depth to the character and situation.
Also the fact that a number of shows still use them today indicates that they are not "a radio thing" as Greenburg and RDA called them.