Yes, it is cheaper
I cannot agree with a point of view that there is not much to improve on water blocks front.
What is available currently is based on two types of design. First and the most popular one is pin/fin type. The other one is impingement type design (Cathar's design and rip-offs).
With warmer CPUs blocks design will have to change to accomodate this and keep silicone at acceptable temps. Sub ambient cooling is a different matter and probably will never go mainstream.
I second 8-ball's point of view towards radiators getting smaller and mre efficient. Mind you, it is dead easy to and cheap to build a setup keeping your coolant at ambient temps or just above it.
TIM interface and generally mounting issues have some potential for improvement since even the best testers do it like 10 mounts and then extract av. values to get close to meaningful performnce values.
Coolants are dead end imo due to massive R&D costs involved.
My two pennies