However, the problem with Android is version fragmentation - a lot of users have phones that they can't trivially upgrade to ICS, and therefore can't use Chrome for Mobile/Android. Asking someone to root their phone and install a custom ROM, and then install a different browser is a bit crazy if you ask me.
True, but both Firefox for Android and Opera Mobile support web workers and work on Android 2.2+. Installing an ICS rom is wholly unnecessary.