Why does Network Restore on my MacBook Air 2012 give me Mountain Lion, not Mavericks I recently upgraded the SSD of my MacBook Air 2012

Very happy with the Network Restore.  Hold CMD+R on start-up, use disk utility to format, and then network restore OSX.

But why does it only offer Mountain Lion?

I then have to upgrade to Mavericks using the App Store.

Which isn't painful, but why couldn't I just restore to Mavericks in the first place?
Internet Recovery will only download the original version of OS X that came with the computer. This is not configurable.

Back when Internet Recovery was released, OS X updates weren't free, so Internet Recovery didn't know if you paid for the upgrade from Lion to Mountain Lion. Therefore it was easiest to just install the original OS X, and then make the user update afterwards.