If your purpose for creating the jQuery UI tooltip is to exactly replicate a native tooltip then your logic is flawless.
But if it is to extend what can be done with tooltips, like this for example:
Then I feel you are incorrect.
If the former is true then that demo should be removed.
If the latter is true then you should really consider implementing something like this:
Many other tooltips have onclick options that will leave the tooltip open (for example) qTip, etc.
For now we will switch to using the one in jQuery Tools, I was trying to avoid that as I really don't much care for jQueyr Tools and was trying to get rid of it. Unfortunately this new project is going live on Monday and it just doesn't look like jQuery UI tooltips are mature enough at this time.
As for the accessibility "claim", it's not a "claim" I know this because I have very poor vision and use a screen magnifier every day, all day, and any elements that disappear like this are beyond frustrating.
Hope this helps.