Obviously it depends on the startup. B2B businesses would get more value out of those connections. I stated that it's likely the biggest benefit of business school, not the only benefit. A true cost-benefit analysis would look also at the knowledge acquired as well as the strength of the alumni network.
I've also learned that there is no one path to entrepreneurship, or programming for the matter. For some people it makes sense to quit school or avoid college. Others follow a more traditional route. There are pros and cons to each. More importantly, it is an extremely personal process. What makes sense for one person does not make sense for another.
As for me, I am very happy in my decision to attend business school. In addition to the networking benefits you pointed to above, I've found that some of the things that I've learned (e.g. Coaching and Mentoring) have wonderful applications to my personal life. Put differently, business school has made me a better father. I plan to write a post on this soon. All the wonderful friendships I built while I was there is icing on the cake.
I should also point out that I didn’t go to business school for the hard skills (i.e. finance, accounting, etc.). You can learn a lot of that by picking up a book. I went to business school to become a better leader and person. Classes like Interpersonal Dynamics (aka "Touchy feely"), High Performance Leadership, and Leadership Coaching and Mentoring are the main reasons I attended business school.
Finally, while at business school, I made an effort to meet and build friendships with brilliant graduate and undergraduate students across all of Stanford. I now know wonderful people that studied CS, Engineering, Earth Sciences, Stats, Medicine, and much more. I feel fortunate to have had the chance to study with all these people.
An MBA doesn't provide you a road map, it gives you a framework of how to approach business questions and an understanding how simple decisions cascade down to all aspects of a company (hr, accounting, operations).
An easy way to see if this is statistically valid, or just something that MBAs tell themselves, is to make a list of 'good' companies (by your personal definition of 'good') and see if the folks who built them had MBAs. The results might be surprising (either way).