In my experience, the problem is that the Android/WP7/[other smartphone OS here] web browsers are so far behind iOS WebKit in terms of functionality that you basically have to handle each device on a case-by-case basis. Given that, a lot of developers choose to focus solely on iOS since it's the lowest-hanging fruit with a massively large userbase and a relatively-standards-compliant codebase.
For example, all mobile web browsers should theoretically throw either a resize or orientationchange event on orientation change, but some Android devices don't, with no other viable fallback, and no clear rhyme or reason as to which devices support it and which don't (other than that newer flagship devices are slightly more likely to be standards-compliant). CSS media queries are more consistently supported, but they aren't the solution to every problem.
For example, all mobile web browsers should theoretically throw either a resize or orientationchange event on orientation change, but some Android devices don't, with no other viable fallback, and no clear rhyme or reason as to which devices support it and which don't (other than that newer flagship devices are slightly more likely to be standards-compliant). CSS media queries are more consistently supported, but they aren't the solution to every problem.