I've heard this argument many times. IBM is doing great, and MS could emulate that, but at a cost. In many ways MS is at a crossroads, where the financial success of the company and their ability to impact the market are on different paths. From a purely business perspective, they should just say: "Office and Windows are mature, we will bug fix/polish the experience for the next 50 years; this is a stable platform for your business." To stay as a mover and shaker, they will need to take their focus off of Office and Windows, and put it on mobile, gaming, and "the cloud". There is no law of nature keeping them from doing everything, but I just don't see it. They can't even get the Windows team to back off of tablets, when Windows Phone 7 is a good fit that deserves a chance.
So how do I explain IBM? They made themselves a stronger company by serving the market rather than driving it. Whether MS is about to join them is a question that will be answered in a few short years.