The question to ask for Rev-Ed actually is, what is the incremental size of the market compared to the effort developing a new product?
There are MANY applications the Picaxe can cover as everyone here is probably well aware of. Also the learning curve is very easy - usually just a few minutes before you have your first LED flashing, and many advanced things are amazingly simple to get running on a Picaxe (try implementing an I2C slave on a raw PIC if you want a comparison, for example). The major shortcomings in my opinion are program structure (no arrays, no user defined functions or parameter passing, etc.), execution speed, and advanced data types and arithmetic (32-bit integers, floating point, strings). But the main market for Rev-Ed does not really need any of this, and many other projects work fine without it as well (or can use workarounds). If the workarounds get too tedious it's time to move up, but again no size will fit all. Some will want to retain some measure of simplicity and choose Micromite, Arduino or similar. Some will chose raw PICs (myself included) or some other bare 8/16/32-bit microcontroller, e.g. some ARM Cortex based offering (in that case, forget "simplicity"). Others will prefer a full-blown computer system like a Raspberry Pi. And so on. So even if Rev-Ed offered SOME system, most people would choose something else in the end. It's just natural that you progress and continue to other things, but on the other hand there is also a steady stream of "new blood" happy with being introduced to microcontrollers in an easy and painful way through the Picaxe (speaking of experience here - I rarely use Picaxe anymore but will never forget it was through the Picaxe I got my entry into embedded programming and design, and keep pointing beginners into that direction, including my own son).
As for the Micromite, as this was the opening of the thread, it is indeed a cute system but won't fit everyone either I suspect since running interpreted Basic it is quite slow (from what I know not much faster than a Picaxe)...
As an aside, I greatly appreciate the very civilized discourse on this forum, which is a major reason a keep returning here, it's very pleasant compared to other forums I am member of. A controversial topic like this would have resulted in mudslinging and name calling after about the second post on most other forums I know!
At least that's my 2 cents.