"In that way it gives Linux an inroad it didn't have before Mono."
No, it doesn't. For internal development you have a wide variety of options. Java is quite good and very popular among those who consider the option of not running their wares under Windows. The only way Mono can appeal to Windows-only houses is by making it possible to run unmodified (and proprietary) products that run under Windows on other platforms.
Were I insane enough to allow my business to run on .NET and Windows, I would only consider migrating it to other platform if I had the assurance of being able to run it unmodified.
And, BTW, as it is, Mono is a patent minefield. Do you really trust Microsoft to act as a responsible corporate citizen when doing the right thing would cut their profits?
I wouldn't even if acting responsible would be profitable. Playing dirty seems too embedded in their corporate DNA.