I would also like to point out that console sales/positioning are not the sole concern of fanboys.
The market share (or at least, perceived market share) of a product amongst its competitors concern stockholders and investors, for starters.
But we consumers don't care much about that. What we do care about is that developers usually would rather develop games for consoles with the largest installed base possible, particularly for games with high development costs (which are normally, though not always, the best games), to guarantee a return on investment.
So yes, attention should be paid to console sales. If you love gaming, and I don't think it's too far-fecthed to propose that the immense majority of users here do, you want to be sure you own the console getting the games you love. A console that sells less will probaly receive less support, hence, you will get less bang for your buck if it is discontinued or does not have a varied enough library to take advantage of its particular capabilities.