It's not a cheaper fan - it's a fundamentally different cooling system. The TB models have two fans with intake vents along the side and exhaust in the hinge (
see this page, scroll about half-way down). The non-TB models rely on a single fan with intake/exhaust vent in the hinge (like a MacBook Air) - they don't have the vents on the side at all.
The 28W CPU in the TB models should be more efficient than the 15W in the non-TB models. The degree to which this impacts a given MacBook would depend entirely on the user's usage - including the tasks they do and even their physical environment (humidity, ambient temps, etc).
Both models have fared incredibly well in benchmarks from reputable sources, with neither model suffering from throttling in common CPU or GPU benchmarks. However, when both the CPU and GPU are under load, they do throttle. And this is where the 28W CPU should start to shine. It should maintain a considerably higher base clock speed under these extreme conditions. It's unlikely, though, that you will stress your MacBook in such a way very frequently.
One thing I don't know is whether the maximum fan speed between non-TB and TB is any different. And if so, what's the decibel difference between 2 fans at say 3000rpm and 1 fan at say 5000rpm. I didn't pay enough attention in physics classes as a kid, it appears.
Not sure if that answers your question, but hopefully a concise bit of information for you.