if you buy a MBA or rMBP 2013, you absolutely need to max out the RAM, as you won't be able to do that later. The reason the Macs are more expensive is that they last longer! Doing the math, you would ultimately spend the same amount on Windows machines over the longer period of time that your Mac remains in good working order. Maxing out the RAM "future-proofs" your laptop. I have a mid 2013 rMBP (13") with 16 GB RAM and the 512 GB SSD. May sound like overkill right now, but I plan to hold onto this laptop for a loooong time.
Apple also offers a govt discount, and that's how I bought my laptop.