"The longer that microsoft wait,the more irrelevant their products become"..........
This is true, but also, the less time there is between updates, the more it undoes their vendor lock in. their customers will get more and more dissatisfied at having to do another expensive upgrade which may break backwards compatibility. There are still many people, companies and institutions running winXP,and there is already talk of windows 8. So while they can't afford to lag behind competition, they also can't afford to release upgrades too quickly. I'm making a guess that their revenues from windows and office sales have been declining. People may,at some point, refuse to spend more of their money on upgrading,and if antagonised by microsoft with lack of updates, they may just start looking towards open source or/and free alternatives. microsoft is a large company and they probably can't afford to sell win8 and office whatever at a competitive enough price to lure new customers,or convince a few existing ones to upgrade.