quantumeffect
There were a number photos from other Ed Sullivan Show performances that showed an overheard mic. This was the only one I found that (I think) was associated with the performance that Rimshot was asking about and showed any sort of mic placement.
Overhead mics were and still are standard TV studio practice. Occasionally you saw floor mics when filming music but overhead booms were used so people on stage could move around unhampered, the view wasn't cluttered and more sound could be picked up with fewer mics. Some recording studios used them too. Johnny Carson's desk mic was just for show ya know.
And the reason they sounded so good might have something to do with using one or two mics that, by today's prices, run in the $15,000 and up category. Also, anything you are hearing today is almost assuredly a digital remake/remaster of the original. To hear the true sound quality of the original record, get it out and play it on a real record player.