Why are you limiting this to navigation features? The watches are far and away more advanced than the bike computers, in terms of exercise features, usability, and navigation to a lesser extent.

* I've been using the Recovery Advisor for 2 years before it appeared in an Edge (the 520).
* Garmin's newest watch supports ANT+ and BT sensors. (HRMs, PMs, cadence sensors, foot pods, etc)
* Edge units typically have a barometer, but can't use it to predict inclement weather without a data connection. Storm Warning is a pretty common feature on most barometric devices.
* Edges lack the sophisticated barometer calibration software in the watches.
* Edge units have no concept of training load.
* Edge units can't tell you what effect a particular exercise had on your fitness level, let alone break it out between your aerobic and anaerobic fitness.
* Edge units can't detect your LTHR.
* I think any of the Edges have wifi?
* I don't think Edges have proximity alerts either?
* I don't believe Edge units have Sight-n-Go.
* Better compass on the watches.