- 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!