You don't even need to root it, just one tweak to your settings and you can download an apk from anywhere you like. If you get your apks this way they aren't market-managed and have no magic kill switch.

Market isn't so much a walled garden but a preferred vendor, in the same way that a Debian repository is.

Gah, so much misinformation. There is no "Kill switch" in Android, the Market App has permission to uninstall applications, it also receives push notifications from market servers that can include instructions to uninstall an app. The Android market is _not_ part of the OS, if you build straight from AOSP you don't get the market app, no app no "kill switch"

Wow, that never occurred to me. User installs malicious app, app roots phone and disables killswitch, user is none the wiser. Game over.