No, why would they bother? Once you are famous/established, no one cares what your credentials are...the PhD only gets the foot in door, and is a useless piece of paper otherwise beyond what you learnt while getting it (disclosure: a PhD whose piece of paper helped him get his foot in the door of a research lab).

Many universities have rules limiting pay and promotion opportunities to people without PhDs.

Maybe at the low end, but definitely not at the high end. As long as they can easily get a position at CMU or Stanford, the university isn't going to low ball them on pay.

Crazily, depending on field, it seems to be an issue even at the high end (see my comment https://news.ycombinator.com/item?id=9144856 ), though my comment is not specifically about CS.

It happened at my university (and I did some moonlighting contracting statistical analyses for some). The salary rules changed to motivate them.

The most mathematically capable geneticists I've ever met (he's at Harvard) was in the same position. PhD-less, was doing great work without it, but ultimately got one at the encouragement of his colleagues. This was gilding the lilly, intellectually, but thanks to rules arcana, probably helpful for career advancement.