A quick question, when do we use HTML5/C++ version?
As long as mobile phone support html5, html5 should be able to run in any platform although the performance is not as good as C++ theoretically.
C++ version does not support wp7 while it works in wp8.

HTML5 version focus on desktop browsers now, and c++ version focus on mobile devices.
We will release c++ with javascript binding sooner.
In other words, for mobile devices, javascript code should run on cocos2d-x + jsbinding, in a native way. The performance would be better than run html5 in mobile browsers.

Does this mean Javascript bindings for all of the currently supported platforms or just Android/iOS (the main platforms at the moment).

only for ios, android and Windows

Is the C++ Javascript bindings the same project as cocos2d-html5 (i.e. use cocos2d-html5 now, wait for c++ bindings for ios/android support)?

Not the same, js binding is a part of cocos2d-x and cocos2d-iPhone, Take a look at the repo https://github.com/cocos2d/cocos2d-x/tree/gles20/js
Cocos2d-html5 alpha version is not ready for commercial games, we will change the API a lot at Beta version.

The final goal is that cocos2d-html5 supports running game code in web browsers and "Cocos2d Javascript binding engine" without or little modification.

Game can be run in mobile browsers with Cocos2d-html5, however, hybrid app has better performance.

What's the difference between current lua support in cocos2d-x and js binding? Any basic ideas to choose which to use in different situation?

Or can I say that js-binding can replace lua?