Hi sledger,
Maybe the link did work - it's just that the site looked a bit "odd" (that's probably me being suspicious, I used to work for a content security company).

Maybe Gary can clarify, but I interpreted his comment, here "An Android app builder would be killer!" as meaning something like,

"Using XWD as a computer-based (ie. desktop or laptop running Windows, Linux or OSX) development environment for Andoid apps would be a killer".

A lot of Android apps are actually developed on another platform and are then "compiled" (or equivalent) for the phone or tablet.

I would totally agree with you that developing small apps directly on an Android device is possible.

Cheers,
SPuD