Those companies generally have a technical ladder that runs parallel to the management ladder.
High-level engineers can have more influence within the company and often earn more than directors and VPs, and most developers who want to move up the ladder don't aspire to become a director or VP -- they'd rather be a Distinguished Engineer, Fellow, etc.
Gates (and Zuckerberg) went to Harvard, and would probably have had a much harder time getting venture capitalists to take them seriously if they did not have Harvard on their resume. They aren't proof that college doesn't matter, they are proof that an elite college matters a lot, but graduating matters a lot less simply than attending and getting access to the network.
I agree with you on Zuckerberg since he was chosen as the winner among a lot of competitors by the VCs. I am not sure what criteria the VCs used.
Microsoft was generating cash by writing interpretors before they brought a VC on board. They only brought in a VC for advice and not money - so they still count. Although Gates' mother also had a lot of contacts in the Seattle upper crust. I doubt Gates needed Harvard outside of finding Ballmer.
Apple got VC funding though contacts made on the job not at school. Jobs went to a Liberal Arts college for less than a year. The Homebrew Club also had a big impact on early Apple. Several members of the Homebrew Club founded companies and they all kept track of each other.
Similarly with Oracle and Larry Ellison. Ellison spent some time at two Chicago universities but his contacts and training were largely on the job.
After thinking about this over night I do believe that the difference between Zuckerberg and Gates is telling.
It used to be that having Harvard on your resume did not mean much in tech since it was not considered a tech school. The feel of the valley changed when John Sculley took over Apple since he was not at all a tech guy. This is just based on my gut, but I saw more Harvard alums after Sculley then before Sculley.
So I looked up the top schools for tech CEOs. This is the ranking of schools with the most CEOs with first round of funding. There were a few surprises for me.
1. Stanford
2. UC Berkeley
3. U of Pennsylvania
4. Harvard
5. MIT
6. Cornell
7. U of Michigan
8. U of Texas
9. Carnagie Mellon
10. IIT
Stanford and Berkeley were not a surprise since I have worked at a bunch of companies founded by Stanford and Berkeley alumni. IIT and MIT were also not surprises.
One thing that skews the results is that a bunch of schools provide masters programs to already successful professionals - so it is not clear that they actually contributed to the success of the alumni.
High-level engineers can have more influence within the company and often earn more than directors and VPs, and most developers who want to move up the ladder don't aspire to become a director or VP -- they'd rather be a Distinguished Engineer, Fellow, etc.