I read with interest a recent Computerworld article, which discusses your worries with respect to declining enrollment in computer science degree programs in the United States. As a computer science faculty member in the closest CS department to Redmond, this is a topic which is also close to my own heart.
Let's face it, unless things have changed drastically in Redmond while I've been away this past year, your technical employees (and those of other companies; this is not unique to Microsoft) put in far more than 40 hours per week. It doesn't matter how interesting that work is; I submit that there is something wrong with an industry that expects its workers, as a permanent state of affairs, to work more than the accepted standard work week. And I think students agree with this and are voting with their feet.
I understand that changing this would have an impact on your company's productivity. However, I also understand that you have been pushing, along with other industry leaders, for increased immigration quotas for technology degree holders. Don't you see that this might be viewed in an adversarial fashion by prospective CS majors? That they would perceive the primary motivation behind this a removal of pressure from technology companies to provide real fixes to CS workers' quality of life? It's true that immigration provides great benefits to universities, companies, and US society, as some of the best and brightest from around the world come here. But there is a difference between bringing in some people to enhance an organization and wanting to bring enough to materially affect the work environment.
In closing, I think that you have an opportunity to set an example and show that your interest here is not merely Microsoft's bottom line -- that you really have a concern for the long-term health of the computing profession and the student pipeline. Why don't you make the 40-hour work week official Microsoft policy, and back it up with measures such as official comp time? Why not evaluate managers poorly if their teams consistently put in more that 40 hours/week on average? Why not put other teeth behind this, to ensure that hours are accurately accounted and that comp time is actually taken? Just because an employee feels that life away from work is important doesn't mean that that employee isn't serious about his or her career. Those are the people who are more like your typical user: the people who may understand how to, as you say, "make things simpler".