well closed loop systems are great because:
1 they fit in smaller systems and (never have any clearance issues with ram or videocards)
2 are easy and light on the motherboard.
3 you can decide where to locate the radiator (i.e. intake for maximum cooling, or exhaust to lower component temps).
4 - for me they can minimize the number of fans in your system - i.e. exhaust is also rad fan
5 - they make builds alot cleaner and easier IMO.
All those PRO's will not be overcome by "competitive" thermal performance from a tower cooler that costs just as much. It better kill closed loop systems on the thermals or its not worth it.