Gosh, really hard to answer. I guess look at the Falcon PC buyers. Lots of money and no need to dig into the tricks for watercooling. Falcon buys it because it's easy to install in an assembly line, they already know their system limitations/configurations etc etc. And maintenance free, very good for less customer service problems.
Good air cooling is a LOT cheaper than water. And it suits a lot of the masses out there for OCing etc. Peeps who build thier own can do much better buying their parts for their systems. Good air is close to an entry WC system for cooling, except the cost. Air is much less when it comes to a high end WC system. The diff is $150 for good air, $400++ for good water. $100 for okay air, $220 for basic water.
No one knows if that system is capable of cooling a Q6600 at 1.5V and 3.5Ghz. If it was the bomb and someone could verify it, then we'd all want one.