You can bet that they will release an iOS app in the coming weeks. As for people on Android 2.x, buy a new phone or yell at your phone manufacturer for not upgrading you to 4.x.

Android 4.x brought some pretty massive changes to APIs and behavior that it is not worth Google's time to continue to support it. They would rather try and push as many people as they can to 4.x.

The posted url opened and worked fine for me on this ipad.

Did Android even have lockscreen widgets before 4? I thought there were only third party lockscreens with widgets before then.

It would seem that they were released in 4.2: http://developer.android.com/about/versions/android-4.2.html

Anyone know whether this is an innovative use of lockscreen widgets by Google, or is this something that's not openly available to other Android devs?

Wondering whether is just a clever app by Google or something that makes it difficult for Evernote et al to compete.

In the comment you are replying to, I linked to an announcement that describes how to make this sort of widget.