I find this rumor dubious, because the preponderance of evidence is to the contrary. Specifically the evidence that revolves around the synch in the development cycle. The farther out the launch the more that doesn't add up in the least. At the earliest the end of this year would work out, and the latest the end of next year. Beyond that you begin to find software development at cross purposes. You have things like studios developing sequels to games they have not launched, and studios with two or even three unreleased titles.
Were this rumor to be true you would see two things. More first party games coming out of Microsoft, because those could be released now, and there would still be plenty of time for a new game to be made for the new platform when it launches. Fewer studios being developed in synch theory. These newer studios are the ones that ought to be developing for even numbered years. I just don't see Microsoft stockpiling that much wealth by going through a terribly long middling spell. Ironically right now they could probably launch this year, and survive off of what they have probably stockpiled so far.
Bottom line is this Microsoft has at least a dozen undisclosed projects in the pipe, and it is really hard to see them existing to fill out the 360. These games are being built with a new platform in mind. Not only are these projects undisclosed, but Microsoft is hiring at a fever pitch. They are revving up rather then throttling down. Microsoft is making a awful lot of noise in gaming for a console two plus years from launch.