Is there a significant reduction in cooling fan noise level in recent MacBooks?
The MacBook Pro with Retina Display received an overall update to pretty much most of the internal architecture. According to Apple the fans, vents and many other internal parts underwent redesign and development.


Apple => High-efficiency fans: Asymmetrically spaced impeller blades and back and side airflow vents work together to move the maximum amount of air while reducing tonal impact.


Personally, I have not had any extensive experience with the Retina models, but according to the statement on Apple's website it can be assumed that the noise should be dramatically reduced in comparison to other previous models.

The MacBook Air has, to my knowledge, received this update. Even after a quick Google search I could not find any 'fan noise' changing events or developments. However, working occasionally on an Air, I cannot complain about any extensively loud fan noises in comparison to my mid-2012 MacBook Pro (non-Retina).