Off topic, but according to [1], web workers have not been available in Android Browser since 2.1. There's a SO Question [2] about this, which points to [3]. Seems crazy, when Chrome for Mobile does support it [4].
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.
They work fine, e.g. on the Nexus 7.