Two things -
First of all- the stock heatsink runs 90C+ at 3.06 GHz, when the 570 LX is installed, my temps never cross 60C at stock voltages and idle is roughly 30 so it does make a big difference (albeit not as much as a true water cooling system). At a 30% overclock with a single set of good fans, low-mid 70's is fine for testing stability as I've never actually seen my rig cross 70 while gaming extensively w/ realtemp gt in the background.
2. I believe the draw of these imitation systems (for myself in particular) is the zero maintainence - as closed loops it's a set and forget until they wear out and you have to replace them. I totally agree that there are much better- efficient cooling solutions, but to each their own. As a last note, my case has 8 fans (all 120mm) plus the 240mm radiator so it's a good representation of a ventilated system - only further proving that a real water cooling setup would push temps lower.