The market share argument just does not cut it. You would think there would be at least one well know case in the wild by now of a linux virus spreading to other linux machines in a sustained and ongoing manner.
What? That's exactly why market-share is so important. You're assuming they can find other linux machines. And how would they do this? How would it discover other machines? This is hard enough to do with a windows host, let alone one that has ~1/100 the market-share.
Microsoft would have to be certifiably insane to consider Ubuntu even a marginal form of competition.
Prove it.
Linux in total represents less then
Microsoft *are* ahead of Ubuntu in at least one, basic, critical area. Stable hardware support that actually works.
Prove it.
Broadcom(or most other) wireless chipsets, nVidia video drivers. The end.
Ubuntu is filled with wonderful software, but honestly it's not ready for wide adoption. Now maybe you can try to pin that on the hardware companies that don't support it, or the users who want to just use what they know, but it doesn't change the fact it's not ready.
If you have a procedure with 10 parameters, you probably missed some.