These days, on larger/newer aircraft at least, GPS navigation is ubiquitous. So [VOR](http://en.wikipedia.org/wiki/VHF_omnidirectional_range)s and [Non-directional Beacons](http://en.wikipedia.org/wiki/Non-directional_beacon) (NDBs) are used less. Wasn't the reason for airways because they were the connection points between VORs and NDBs?

It seems like a pilot could easily "fly direct" from one airport to another without using any intermediary checkpoints. And yet I've been told on several occasions that most pilots use airways. 

Why do pilots still use airways instead of flying direct?