- Hardware support (you really3x can't beat this)
- User Interface (excluding Apple Mac Os X)
You may flame about anything, but I think that's a fact. Risk? of course there is a risk from become popular like MS Windows, so does if other OS get it.
About why OSS, you may follow this links:
www.nosoftwarepatents.com --> a serious issue if your read carefully
www.gnu.org --> common license explanation
www.opensource.org --> more license explanation
Other may see a general fact that most OSS are free (at no cost)
:)
BTW, its not 90's anymore. Look at sourceforge and see how much OSS has grow.
With better education and better programming language for novices/non-programmer, in 10's thing will get more exciting. OSS will prospering in every type of software, I hope!