Microsoft (either explicitly or de-facto) owns the Common Language Runtime, the C# language, Entity Framework, ASP.NET, IIS, Windows OS, Windows Phone OS, XBOX, XBOX live, etc.
An example that I think of is LINQ (not linq-to-sql, mind you, but the language-integrated query stuff). So many things were required to make LINQ viable in the language and the tools, etc. that it doesn't seem realistic to expect an external dev team to throw something like that together. That stands in contrast to things like test automation, which nUnit had already been doing very well for years before Visual Studio tried to get into it.
I'm really not sure any of those is something only Microsoft could do, much less in the restricted scope of development tools.
When you say "that it doesn't seem realistic to expect an external dev team to throw something like that together", you are giving Microsoft's internal teams a power they simply don't have outside their very narrow zone of influence, as there is a lot of stuff being done outside it.
An example that I think of is LINQ (not linq-to-sql, mind you, but the language-integrated query stuff). So many things were required to make LINQ viable in the language and the tools, etc. that it doesn't seem realistic to expect an external dev team to throw something like that together. That stands in contrast to things like test automation, which nUnit had already been doing very well for years before Visual Studio tried to get into it.