The "browser usage" market share is a very inaccurate and pointless stat by default. Do developers really care if a user uses 5 hours a day his browser or 1 hour? Wouldn't they care more about how many use a certain browser?

Especially on the mobile side, the stats get very skewed, because browser usage will be much higher on a tablet (read: iPad) than on a smartphone (iPhone/Android/Symbian/whatever). So say 10 million iPads could get as much "browser usage share" as 50 million iPhones. The iPads, although much fewer than iPhones, could easily double up the "iOS Safari" market share in this type of stat. That's why these stats don't make any sense.