That means they are unable to deliver the same quality across multiple platforms, still want to sell their software to Mac/Windows customers.
Having fought against both Windows and Mac about what my work machine should be, I can certainly see why a developer may need less support on a Linux machine. Linux (and traditional unixes in general) allow the owner to make everything work the way he/she thinks would be more appropriate.
A simple example:
One of the types of apps you can build with our tool is Python/PyGTK apps. The root benefit here is that, because Python is interpreted, there is no compile time -- when you click "Run" you instantly get to start testing your app out.
Because Python and PyGTK are readily available in just about every distro's repo, this is never an issue. But, on the flip-side, setting up Python/GTK/PyGTK on Win/Mac can be a bit of a nightmare even for the nerdiest among us.
(We provide our "HTML5" web app option as the default option on Mac and Win for this very reason... But, even then, we still get support requests on trouble-shooting someone's Mac where PyGTK just won't work quite right.)