Ok, I need to make an addition to the eating stuff... High Elves and Night Elves indeed eat. Check WoW! They have food there! However, I think that mana regeneration is important! I believe mana is the source of line! Without mana (and magic) you can't live! And I think that through sleep, you regenerate your mana, because entering Ysera's world, you regenerate mana. However, High Elves and Night Elves had their sources of magic, much more powerful than plain sleeping. I think that is why Blood Elves still do not sleep. They are not used to it, they need a power source of magic such as the Sunwell...
Anywayz, this is just a theory but I really wanted to mention it here!
~Daelin