GitHub now [allows HTTPS pushes][1], so a man-in-the-middle attack on a single connection would be sufficient to push backdoors. In any case, can't the intermediary just add another SSH key to the account?
I doubt anyone would have used CSS in 1996, and "FrontPage 6.0 [2003]" did not exist back then. FrontPage might have only been used as part of the archival process (for removing links to dynamically generated pages and other excluded content and adding a fourth footer line to every page).
1) Increase Linux's usage share, and we will see a greater share of Linux exploits and malware. Case in point: Mozilla Firefox.
2) New versions of Windows have long retained backward compatibility with older applications (the upgrade from 98/ME to XP an exception largely necessary for security).
Just as importantly, Microsoft supports their operating systems for at least ten years after their initial release dates. In contrast, Ubuntu LTS releases are only supported for five years (and until 12.04 comes out, only three years on the desktop).
Keep in mind that upgrading software costs a business money, and rewriting (parts of) it to run on a totally different OS costs even more. No wonder why Windows is the business OS of choice.
In general, it's not a new idea; software companies have long sold expensive authoring software for their free viewer programs. Shockwave, Flash, QuickTime, RealPlayer, and Viewpoint have all tried to use this business model for browser plug-ins. However, it's the most direct attempt I've seen to apply the business model to an already open standard.
[1]: https://help.github.com/articles/pushing-to-a-remote