Because it's obviously a fair comparison when you compare sales of 300 different model phones that all have Android OS to 4 model phones with iOS. Yes... that's a good comparison. Compare one phone's sales to another phone. I don't know what the numbers will be, but that's a legitimate comparison.

The most recent article I could find was for May 2011, which showed iPhone 4 being the #1 phone for sales (up 3 places from the month before)