Even if you only get 2 ticks of W, that's still pretty much free damage because of its huge range and the fact that you can drop it and back away while it does its thing, plus you're depriving the enemy of a place to stand while they try to last hit. A few levels and/or some AP and you'll be farming most of the wave of creeps with that, too, and the only way for them to avoid it completely is to not stand in the minions, which opens them up for getting hit by Q->W or even W->Q. It's good harass because it's really safe, plus you can use it to spell vamp back any health loss from the enemy harass, as well.

She was also buffed indirectly by Spirit Visage applying to Spell Vamp, actually making it a great item for her now, especially if you have some other source of spell vamp, like a WotA or just a Hextech Revolver. I've actually had a game where I had 98% spell vamp because of passive + WotA + Hextech Gunblade (normally I don't get this, but had way too much money) + Spirit Visage, and that makes you almost impossible to kill. I was ending fights against a Karthus with Sorcerer's Boots and 5 deathcaps with full health. (Although I don't understand getting more than one deathcap when Archangel's Staff usually gives more AP for less gold than any extra ones.)

W is not free damage. The mana cost on it is far too high to consider it for use as zoning or harassment effectively. Also, if you back off, you deprive yourself of experience and the enemy champ can just walk around the pool and proceed to last hit.

You're right about her sustain though. By all means, she can survive for extremely long periods of time. But you also have to note that without AP, her damage really falls off and she becomes a stun/shield bot.

I always start with Meki Pendant + 2 mana potions, then grab Tear and Chalice, so mana is pretty much a non-issue, and when I said back off, I meant outside of the enemy's immediate attack range once they exit the pool. You kind of have to build her specifically for sustained harassment if that's what you want and pretty much give up your chance of getting kills unless they are seriously overextending, but the option is there and it can be an effective one, especially if you are in mid with the enemy team's only carry and forcing them to constantly turret hug and/or return to base to heal. It is also true that she does wind up mostly there for stuns/roots/shields/mr-shred in team fights with this build, but she also draws fire off her team mates which she can heal right back, so she's kind of an off tank. You'll also probably have a huge exp advantage over everyone else, (I've been 4 levels above everyone else before with 0 kills) so mid game you can be a pretty dominant force.

More specifically, my build order is Tear, Chalice, Boots of Speed, Hextech Revolver, Spirit Visage, WotA (from revolver), Ionian Boots, Archangel's Staff, Rabadon's Deathcap if I've become the carry, or an appropriate aura item if someone else has. W,Q,E, then R>W>E>Q. It's a little different, but gets the job done in a subtle way.

Shurelya already stated that the CD on morganas and luxes bindings are being buffed. along with morganas movement speed, if you ask me the only necessary morgana buff is to buff the speed other then that shes perfectly fine.