As far as i know, XNA express is a free software.
Yes... but it's also made by Microsoft.
I really don't know how the whole licensing/quality control thing works though, so maybe it wouldn't be an issue. That Action Game Maker thing doesn't seem terribly professional, judging from how their website is written*. So who knows... maybe any Tom, ***** or Harry can make a program that makes 360 games.
What would definitely be an issue though is the work it would take to make Construct export 360 games.
*(Might just be a translation issue though)