Android fragmentation is worse than web fragmentation. On the web one only has to test on 4 browsers x two operating systems, as opposed to dozens of phones x several os versions x several carriers.
And of course the 4/2 argument is bunk anyway. Web developers test ever major version of every browser (especially with IE) and every version of every OS. So for example it's {XP,Vista,7} cross {ChromeN,ChromeN-1,IE7,IE8,IE9,FirefoxN,FirefoxN-1} plus {Lion,Snow Leopard,Leopard} cross {Safari,ChromeN,ChromeN-1,FirefoxN,FirefoxN-1}, etc...
You can't have your argument both ways, basically: either the small market platform variants matter or they don't. If they don't, Android support is easier than the web by a significant margin.
And it depends on your audience. For instance, if you're Reddit (or are targeting the Reddit users) you're looking at 7% on IE, and 2% on Opera. You can practically ignore those browsers in that case.
I bet the Reddit crowd are almost all up-to-date with whatever browser they are running. A stodgy enterprise or gov't office might mandate a certain outdated version for internal apps. I'd bet that a small slice of the vast number of websites out there actually target the average user. The ones that do are likely generic portal ("start page") sites, stores with broad appeal (Amazon, Target, B&N), or public services that everybody would access.
I could be wrong, but don't Chrome, Firefox, and even Opera now auto-update as well?
At the end of the day we have to much less checking in web development than we do in mobile because while browsers are different that are more alike than they are different. That cannot be said for Android/iOS, they differ down to their very core and most cross-platform attempts fall hopelessly short of a usable app.
The point was that the added cost to development due to platform incompatibilities is less than it is in the web world. And I think that's largely inarguable. Where is the list of Android incompatibilities that is anywhere near as complicated or exhaustive as http://caniuse.com for example? People in this thread are having a lot of trouble coming up with any specifics at all, in fact. Mostly just a list of apps that break somewhere; no one seems to actually remember any real bugs or workarounds.
On the web one only has to test on 4 browsers x two operating systems. On Android, one only has to test on 1 browser and 1 operating system.
Not true. Each carrier has their own build of the OS, and they have different sets of bugs. For example, on one of the Samsung phones (I don't remember which one) on one carrier there's a loopback interface, and on another carrier there is none.