Oh my goodness. Double post.
Better make use of it then... Why is Akatosh mad?
Lord Hyamentar, http://www.gamesas.com/bgsforums/index.php?showtopic=702787#. (Post #12)
Now, as for the original question of "what are myth-echoes", I would describe them as follows:
"Myth echo" is TES jargon for a frequently used real world literary technique known as an "allusion", except in TES, intentional allusions gain actual power from what they are "alluding" to.
For example, Aslan the Lion has been said to be an allegorical Christ figure in C.S. Lewis' "Chronicles of Narnia" series, although no one said it outright. When Aslan was slain in the traitors stead by Jadis the White Queen, Aslan was resurrected awhile later due to his noble sacrifice. This was the allusion to Christ.
Now, if we were told ahead of time that Aslan was an allusion to Christ, we would not have worried about him being killed in the traitors stead, because those that know the story of Christ would set comfortably back and await his return. Eventually, Aslan states that he goes by a different name on Earth, which is now effectively stating that Aslan is no longer an allegory for Christ, but that he actually IS Christ, simply in another aspect.
The question then becomes, was Aslan Christ from the beginning, or did he become Christ through his actions?
Although I apologize for bringing non-TES stories into the picture, especially in that my example involves real-world religions, I must say I believe that we are making myth-echoes too hard of a concept than necessary.
In TES, being an allusion is the first step to becoming the thing originally alluded to.
Yours in the Scrolls,
___The Word Merchant of Julianos