But I think it does matter in another sense. The phone I had before iPhone was a Sony Ericsson T610 (
http://en.wikipedia.org/wiki/Sony_Ericsson_T610). What OS did it run you ask? Hell, I don't even care. If you looked it up and told me, I still wouldn't care. If you told me it was 0.00001% of the market share, I STILL wouldn't care. That was a freaking awesome cellphone and you aren't going to convince me of anything with market share graphs or Open Source business models.
However, if I bought that same class of phone, it would probably be running some derivative of Android. As near as I can tell, every phone Sony makes now is Android. Does that mean I CARE that it runs Android? Did I CHOOSE Android as my life goal in buying the phone? Hell no. Just like I don't care what my T610 ran, I also don't care what generic android device #6411 runs. In other words, if I choose to be loyal to Sony Ericsson based on my positive experience with the T610, I probably have no choice but to get an Android phone now. Not every phone is the Samsung Jesus SII that died for your closed source sins.
I know its hard for some people to grasp, and I'm not talking to anyone directly, but not everyone picks a cellphone based on the OS. The fact that Android is a cheaper solution than rolling your own Cell OS gives it higher numbers, but that doesn't mean it's the consumer's choice. Conversely, people are choosing the iPhone because it's an iPhone probably every time; or at least arguably more often.