IF I'm understanding you properly (and "completed in some way" is total gibberish I cannot decipher) you are pointing at the only scenario where the title attribute makes any sense -- conveying more information than the content of an element can.
Problem with that is I've always said if the content of an element doesn't convey the full meaning, it's the wrong content in the first place!
... and in the case of image replacement it IS redundant BECAUSE YOU ARE PUTTING THE IMAGE OVER THE TEXT. If the image does not convey the same meaning as the text it is going over, It's the wrong image!
Take the original:
<li><a id="home" href="http://xyz.com/"><em><img src="1/1.gif" alt="link home page" /></em><span></span></a></li>
The alt text should be there so images off you know what it is -- though the text 'link' and that it might go to a 'page' is redundant since it's inside an anchor and the anchor should be conveying either visually or by the screen reader that it's a LINK that might actually go somewhere.
In my rewrite:
<li class="home"><a href="/">Home<span></span></li>
All the information that needs to be conveyed is there. An anchor that takes you home. Images off/CSS on or CSS off you'll see the text "home" -- that's what alt text is for. Images off users. That some other browsers (IE) use it for a tooltip does not mean that's what it's for -- and many developers have gone out of their way to make the IE tooltips and other stuff (like the img menu) NOT appear on their images when the images are PRESENTATIONAL.
Exactly the situation we have here. The images are presentational affectations applied to the text, as such they should NOT behave like IMG tags in the first place! If we wanted them to, they'd be IMG tags. That would be like trying to find a way to make our border images have alt text too.
The WDG's HTML reference page explains it best:
The required ALT attribute provides alternate text for those not loading images. Effective ALT text should generally give the function of the image rather than a description of the image. For example, ALT="Welcome to XYZ Corp." would be more appropriate than ALT="XYZ Corp. Logo" for a company's logo on its welcome page. Good ALT text is crucial to the document's accessibility for users who do not load images; see Use of ALT texts in IMGs for a thorough discussion.
As to slapping TITLE on it and calling it an enhancement, don't you find title tooltips a bit annoying when dumbasses put them on things like menus? I mean every time I see code like this:
<a href="\" title="Home">Home</a>
I feel like smacking whoever did it around like a baby-back *****. Here's a tip, if the title attribute of an element has the exact same content AS the element it's on, there's no reason to be using the title attribute. See the millions of bandwidth hogging garbage turdpress templates for examples of that idiocy in action.