I mean, you can get a 13" laptop from Dell for $600. Sure it's a Dell, and it has a HDD instead of an SSD, and battery life is like 1/2 the rMBP, it's thicker, but it's also 1/3 the price. Somehow I don't think it costs Apple $1200 for a higher-res screen, battery, and small SSD.
Ahh, yea and you're also stuck with Windows and 12 months of McAfee Virus Scan. Sounds sweet.
Everyone wants to compare price with Windows PC's and Macs and completely leave out the fact that they don't run the same OS. OS X is a premium operating system, with excellent included software, and is much less susceptible to adware, spyware, and viruses. You also get a clean machine without the bloatware and "Intel Inside" stickers all over the place.
$600 Dell laptops are cheap, poorly constructed, and have horrible resale value after a few years. Keep in mind that your $1,600 rMBP will still be worth more than that Dell in 3 years and you can sell it for something new.