There is no way that carrying a slightly more weighty bumbag is going to effect someone's performance so I disagree with the cheating thing. Also the front of the field spend far less time in the hills than the back during a race so arguably have less need of all the gubbins. They will almost certainly know the route better and overall be more experienced of the hills too. The overriding issue is eff all to do with cheating but all to do with the race organiser's responsibility to ensure that safety issues are covered and, should someone die during a race, no blame is pinned on the race organiser. If they say carry it, just carry it.... but its nothing to do with cheating.