^ A coincident pair does produce a fundamentally different "flavor" of stereo, further influenced by the particular implementation M/S in the stereo unit via the MEMS mic elements, but there may be other reasons as well..
Most tapers are probably running two mono units. The mono unit came out first and represented less of a gamble, and the technical specs for the mono unit or the stereo unit when used in mono mode is somewhat better. Also, the use of two mono units allows for stealth concert recording microphone configurations that are well understood, liked, and long relied upon by tapers.
For a long while there were no decent concert recordings samples of the M/S stereo unit, so until recently it's stereo qualities in concert recording situations remained unknown.
The individual nature of the small units allows for use as spot-mics or close-mics, either reinforcing a primary stereo pair or building a mix outright via panning. That kind of use naturally lends itself to a number of units,
Some may be using them in more advanced, purposefully arranged stereo arrays. Common examples include: 3 mono units positioned as an L/C/R mic triplet, or a mid/side stereo unit placed in the center between a couple spaced omni units. Others include multiple stereo units, or various combinations of stereo and mono units. I've been considering picking up multiple units for that kind of use, and for spot-mic'ing when needed.
