That is due to the market these things are sold into. The entire MDK-ARM product is based around a Device Database which contains details of not only the core but the memory maps and peripherals of the device. It is being in this database that is classed as 'supported' for the product as it means that the libraries that are supplied with MDK-ARM will just work(tm).
RVDS is more aimed at SoC bring up and doesn't have such a database.
As has been repeated said the compiler in MDK-ARM is armcc. The only difference is that some flags have been disabled so it can only be configured to tune code for ARM7,ARM9 and Cortex M and R profile cores.
-p