I agree, GPU subsystems have much high TDP designs than CPUs nowadays, 300W vs 150W not to mention the placement often causes that heat being trapped in the chassis.Multi gfx card setups benefit most from water-cooling as do more extreme cpu overclocks...
That said with FSB gone and blck overclocks being extremely small... I have not done much cpu overclocking lately.
The most I have ever spent on a waterloop was $500 and it was quite effective.
I wish more companies made rotated motherboard cases like Silverstone where cards can directly vent up