I suspect that letting people do their own thing when it comes to placing content on the web is based on two historical features of Microsoft.
The first is that because many Microsoft employees were strongly engaged with computers, there were many early adopters of the internet and more importantly the web (Microsoft.com registered in 1991). I suspect that the anything goes culture of the wild west days of the web persists to some degree within the organization.
The second historical factor is that there were a lot of employees with fuck you money during the early days of Microsoft's web presence and Microsoft management didn't waste resources forcing developers to heel to the sacred ideas of branding experts.
If you dig around Microsoft, you will find lots of standard tools - e.g. MSDN has a fairly consistent graphic presentation when it comes to technical documentation - it just looks nothing like Channel9. However, these differences, while not ideal for consumers, are pretty much irrelevant when it comes to supporting developers.
Yes the bitmap code snippets are embarrassing but not in a Facebook security hole kind of way. Any developer doing .NET programming isn't going to be greatly slowed down by typing in the code rather than copying and pasting from the MSDN page.
