I was having issues with my HTC missing out segments due to the poor GPS chip in it, so at one point in the summer i was running with HTC and a Iphone 3gs (no sim) both logging the route.
Both phones picked up different segments as well as the main core ones, and the times were different upto 1 minute for some short segments even.
The overall distance was around half a mile within each over a 20 mile route.
I have come to the conclusion Strava via a mobile is only a guide only.