There are plenty of pretty and capable air coolers but ultimately the balance of thermal performance, acoustics and aesthetics of water cooling is untouchable. I don't think any single thing on it's own make it justifiable but when appropriately specified the combination of what can be achieved is impressive.
For a gaming focused machine i'd actually be inclined to agree that the benefits of water cooling a CPU really aren't well founded, add in a GPU however and then it's a different matter. That kind of expand-ability and the quality these kits offer makes a lot of sense. I've used both EK's kits and the Predator in builds for friends and actually I prefer the kit, ultimately the pump seems just a little quieter being completely isolated. It's actually easier to make it super neat as well whereas it takes a little effort to cut down the tubing and refill a predator for a small system.
JR