Does this even matter in this context? It appears that Evernote provides all the platform specific software for free, the Android app is listed as free in the Market. The service is free no matter what platform you use, and the ability to "go premium" doesn't have a condition for platform either. There are many Linux users who pay for on-line services, like Evernote is. Flickr pro accounts would be one example, and there is no flickr provided uploader app (which are free on other platforms too) that runs on Linux.
The chance that Linux users would or would not pay for software have nothing to do with the lack of a native, supported client for a specific platform when all the other platforms are provided for free. The choice to build software you're going to distribute for free for your userbase should be based on the platforms the userbase is using, not if they would pay for something that you aren't going to charge for anyway.
The chance that Linux users would or would not pay for software have nothing to do with the lack of a native, supported client for a specific platform when all the other platforms are provided for free. The choice to build software you're going to distribute for free for your userbase should be based on the platforms the userbase is using, not if they would pay for something that you aren't going to charge for anyway.