The current LE version is 7, v6 is no longer being updated with the last patch being issued in July 2012, you can upgrade to Cubase 7 Essentials from AI 6 for under 40 euros and to from LE 6 for under 50 Euros, which in addition to being currently supported is much more powerful than LE/AI. Logic is considerably more expensive than that.
In addition to that the people who bought logic express 9 will not get an upgrade that works with OSX 10.9 and no upgrade pricing to either the full version of 9 or any subsequent version, they will have to start from scratch. So all in all I think it is wiser to continue on the Cubase upgrade path than jump onto Logic given recent history.