Unless you have issues with the weight of the 15", you will see little performance difference between the MBA and the 13" rMBP for your uses. You won't be pushing a quad core processor in any way based on what you do so why even bother with the 13"? If you really want to take advantage of the money, get the 13" rMBP only and save the difference. Max out the RAM and SSD and enjoy. I just don't see a performance need listed for the 15" retina with dedicated GPU and a huge additional expense. Or add an iPad for mobility and the rMPB 13 for more general use.
If it were me I'd be looking to save dad a few dollars. If he truly isn't interested in saving money on the deal, buy whatever you like most.