In article , Bob Gardner
wrote:

An article (actually, a sidebar to an article) in the July IFR magazine says
"According to AIM 1-1-20 (f)(7), by omission, you can't just input the VOR
as the active waypoint....," and "...according to this passage, the FAA
allows GPS to substitute for everything except for a VOR. For some reason,
the FAA has faith in its VORs and won't let you substitute GPS for them as a
primary means of navigation."
Maybe this is why Garmin does not include VOR-based airways.

Not to mention the software updates required to keep the airways
current.