I tried out my Garmin eTrex20 lastnight to plot a route from my house to Edinburgh for work. First I set the route finder thingy to bicycle, and it routed me along the A90 off the Forth Road Bridge, a 3 lane near motorway which has well established and signposting which excludes pedestrians, bicycles, horse drwan carrages etc... I set the mode to pedestrian and the route remained unchanged. Funny as it set off from my house and in both cases found a long cut (opp of a short cut) round the back of my estate on a bumpy path through an industrial estate which I knew of already. So now I know not to use the 'where to' route finder on Garmin devices as it either routes me down a (nearly) motorway or on long convoluted overgrown paths instead or parallel along a quiet road.
I hate to say it, but whats crying out here is a partnership between Google and Garmin for route finding where, for instance, with a Wifi connection the device could use Googles pedestrian route finding online to find a safe route thereby reducing the processing overheads of the onboard cpu etc...