Moderator Post (s) for this thread: >I doubt itbyDanO on 09/26/2007
** Which is surprising, seeing that 24-in. and smaller ranges exist. Range hoods for that size are available. **
Yes there are 20", 36" and 42" ranges but none of them have a corresponding sized micro/hood available for them. 30" inch is the most common range size and likely to have the most need for a mating micro/hood combination.
It is costly to build a product which will only have limited market appeal.
There are some stands available for mounting a microwave above a range (see the following link) but not in a combination with a vent hood.