It does matter, especially when you have Microsoft crippling the web with their consistently outdated browsers. Just look at what WinPhone7 is running compared to everyone else's webkit-based solutions. Even when they get their ie9 on the phone it will still be behind the browsers in ios, android (including firefox and opera), and the newer blackberries.

We'll be writing if(ie) conditionals for a long time if people start buying winphone 7