Android is fragmented, not just because Android devices have different screen sizes and resolutions, but also because they have different input methods as well (some are fully multi-touch, some have back/home button, some have QWERTY keyboard, some have stylus, ...) AND are usually a couple versions behind (just 1.2% of Android devices run 5-month-old 4.0, compared to about 60% of iOS devices that run 4-month-old 5.0[1]). I guess a huge portion of OS X users are on Lion or Snow Leopard (if I had to throw a number out of my hat I'd say 45% on SL and 35% on Lion; but the important thing is that every new Mac sold in the past 6 months came with Lion, not Android 3.2!).
And back to the screen size fragmentation point he's trying to make, I think it's really not as severe on desktop as it is on mobile devices - if you fine-tune a FULL SCREEN mobile app for a 4.1-inch display, it wouldn't fit well in a 4.6- or 3.5-inch display, and will look like garbage. But if you fine-tune an app for an 11" MacBook Air display, it's still reasonably tolerable on a 13" MBP.
And back to the screen size fragmentation point he's trying to make, I think it's really not as severe on desktop as it is on mobile devices - if you fine-tune a FULL SCREEN mobile app for a 4.1-inch display, it wouldn't fit well in a 4.6- or 3.5-inch display, and will look like garbage. But if you fine-tune an app for an 11" MacBook Air display, it's still reasonably tolerable on a 13" MBP.
[1] http://www.macrumors.com/2012/03/23/developer-sees-quick-ado...