I've found a site which seeks to explain this - www.mrm-explained.com.
There is lots of useful info on this site and i'd encourage anyone interested in the subject to pay a visit and find out more. Clearly the definition of what MRM is needs to be flexible - my organisation (www.marketingqed.com) is building out our own marketing decision and analysis platform and some clients consider what we do a form of MRM. Clearly we're looking to go beyond the classic reporting function. We're also unlikely to adopt purchase approval process as tools from organisations such as Aprimo and Unica already manage these exceptionally well. The difference we will offer will come through superior analytical tools and more interactive simulation options - my greatest issue with many MRM systems is that they often end up as glorified reporting tools - SAP or Oracle for marcoms. I believe that clients really want help answering their questions rather than more pieces of info to print out - ie - no more "TPS reports".