Using open libraries would make it easier to port from Win to Lin. It's not about "omgomg linux support" it's about a people's platform. We're spending thousands on computers, more on software, so it's nice to know there is a free operating system that allows people who can't afford Windows (or simply don't want to use it, or can't use it, etc) to be able to get work done. It's everywhere. It's already in most consumer electronics for its ease of use for developers (and extremely low cost of $0.00, that's USD) and it's what powers Android.
C2 may be the best software out there for designing HTML5 games, but all the others (except Game Maker) have a Linux version.
For me it's not a question of price, but of openness and pervasiveness. I'd gladly pay $500 for a version of linux as powerful as windows in all regards - the only reason I haven't switched is because
- linux can be a bit funky requiring you to use the shell for some tasks (configuring X being one of them). Ubuntu is definitely making things better in this front, but not fast enough.
- The software available isn't up to par. I miss adobe's Photoshop/Illustrator/InDesign/AfterEffects as well as Microsoft's Office suite. I also hate that none of my game dev tools are available for linux (not just C2, but also articy:draft).
I wish I could change to linux. I'd never look back.