considering the rMBP is the same thickness and only a lb heavier than the 13" MBA it is easy to compare them. Price is not an issue with some people.
Well if are actually compare price MBA 13' with 2.0Ghz processor, 8 gig ram, 256 SSD the price quickly becomes $1700.. so that why when looking at getting an upgraded MBA or a rMBP they are comparable.
Price aside
display
The macbook air is a 13" 1440 by 900 resolution
The rMBP is a 15" 2880-by-1800 resolution
That's
twice the resolution on a bigger display.
Storage
The macbook air offers 128, 256 or 512 gb of flash storage
The rMBP offers 256, 512, 768 gb of flash storage
Notice how you can't get a 128gb drive in the rMBP or a 768 gb drive in the MBA
CPU
MBA 2.0 GHz core i7
Dual core with turbo boost to 3.2 GHz.
rMBP 2.3 GHz core i7
Quad-core with turbo boost to 3.3 Ghz
Dual-core vs. Quad-core
Memory
MBA
Standard is 4gb Max is 8gb
rMBP
Standard is 8 gb Max is 16gb
Size and weight
MBA
Height: 0.3-1.7 cm (0.11-0.68 inch)
Width: 32.5 cm (12.8 inches)
Depth: 22.7 cm (8.94 inches)
Weight: 1.35 kg (
2.96 pounds)
rMBP
Height: 0.71 inch (1.8 cm)
Width: 14.13 inches (35.89 cm)
Depth: 9.73 inches (24.71 cm)
Weight:
4.46 pounds (2.02 kg)
The rMBP is
1.5 pound heavier then the 13" MBA
Graphics
MBA Integrated Intel HD 4000
rMBP Integrated Intel HD 4000
+ Nvidia GeForce GT650M 1gb
Integrated graphics vs. discrete graphics is completely different.
This highlights the biggest differences. These machines are in no way comparable. Users who buy a 13" macbook air do not have the same needs as those who buy a rMBP.