Limitation is based on the minimum of the SDK you build against (Fortunately, for 3.1.0, you can only build against 5.1 and later due to XCodes supported) and on the device OS.

That is, if you use a too-old SDK, Titanium will most likely be unable to link to necessary libraries and so fails gracefully. If you're on an old OS device, Titanium will detect that and not try to do something the OS can't handle.

I'll add in the text into the descriptions, but I want to leave the OSVer in, even if it's not displayed, as it might be of use with other things that may rely on the docs as a spec (EG, code processor)