The new IBM follows the business model you just mentioned though they do not venture outside technology. They no longer invest in building anything ground up. They buy a reasonably successful technologies ( Lotus, Rational, etc) and use an army of salespeople to upsell the new technologies.
http://en.wikipedia.org/wiki/List_of_mergers_and_acquisition...
The reason IBM does not get outside the technology sector is because the profit margins are one of the highest when it comes to software. They have sold most of their non-software business's in recent years: They dumped the loss making Thinkpad for a hefty sum to Lenovo, got rid of most of their semiconductor business and are a software sales company today. I guess the same reason will apply to MS for not getting into any non technology sector.