Mac OS users and especially Mac OS developers are a proud lot. Users who were around since the dark days of OS 8.x watched their favorite platform shrink in market share to near irrelevancy in the computer market had their faiths tested again and again. I understand that. Up until OS 8.x I pretty much felt the same way (though market share wasn’t the only reason my passion was cooled).
I can also understand why some Mac OS developers focus solely on Mac OS X development. For one, if you are a professional developer and only supporting the one platform, you code in Xcode and probably are coding in Objective-C. C derivative languages require a huge investment to learn. There are RAD tools that will let you create software for the Mac without a comprehensive study of professional software development – not Objective-C. And Objective-C really isn’t very portable to other platforms anyway. That’s why many Mac OS developers use the more portable C++ instead.
So if a developer creates an application on the Mac that leverages all the most current, interesting features exposed through the lastest OS update, without any consideration of porting to Windows or Linux – yeah, I get it. There are plenty of application categories where it may not bring any particular benefit. For example, a specialized word processor (for instance, ones focused on novel writing) that is Mac OS only is understandable, especially if it supports exporting to any number of open standards (or at least one that can be read my Microsoft Word).
The ones I do not understand are ones that would benefit from cross platform collaboration, such as project management software. Omni Group, a well known Mac OS developer, developed a product called OmniPlan. This follows in the steps of another very good tool called Merlin from Project Wizards, that unfortunately is also Mac OS only. You really need to be in an all Mac shop to pull this off – anyone who is a collaborator within your own company is going to need a Mac just to use this software. Yes, there are quite a number of all Mac using companies, so at this level it may not be such a bit issue. But this problem extends beyond simple choice but also into specifics of your industry. In many industries, clients are also collaborators, and can you reasonably expect your clients to also be Mac only?