Fragmentation is something developers have had to deal with forever. Your Windows app needs to run on Windows versions including XP, Vista, 7, 8 Server 2003 and 2008, 32-bit and 64-bit. Also there are a multiple screen sizes and aspect ratios.
The same holds true for Websites. It must work on multiple browsers and multiple versions of browsers.
I can only think of 2 cases where developers were able to avoid some form of fragmentation.
1. When IE 6 held 90%+ of the market
2. iPhone before the iPad
Even now your IOS apps need to support multiple versions of IOS even if 50%+ are on the latest. There are 2 pixel densities on iPhone and iPad, there are 2 aspect ratios on iPhone. Also each device has a portrait and landscape mode which need to be handled differently.
A developer needs to consider all of these but the majority of the fragmentation issues are handled by the OS and APIs. You can write an app with the latest APIs and it knows how to deal with the various versions of Android. There are layout schemes for dealing with different screen sizes and aspect ratios.
The only people I can think who are complaining about fragmentation are developers who built iPhone apps in the early days where they had no fragmentation to deal with. I suspect most of these people were not developers before iPhone so never had to deal with fragmentation issues that have always existed.
You can probably handle 90-95% of Android devices by just taking minor and standardized steps for dealing with fragmentation. People playing the fragmentation card should shut-up and stop spreading FUD.