Yeah, of course the two markets and products are different. That doesn't excuse GNU/Linux entirely though.
The Android team managed to convince application developers to write for their platform, despite it being new. This something Linux distributions have never been able to do, and it's clear that without application developer outreach and coordination, no mobile or desktop platform can survive.
People simply don't buy smartphones with a lousy app ecosystem. Windows Phone 7 is testament to that. There are some really nice Windows 7 phones, but the platform is struggling. Microsoft is putting most of their effort into convincing developers to support their platform.
Similarly, most people would be unsatisfied with the application ecosystem of Linux, which explains why OEMs and consumers seem to show little desire for pre-installed Linux systems. What concerted effort has their really been by Linux distributions to convince developers to write for our platform?