not all trails are equal, some are more prone to damage during the wet season due to the loam factor, drainage, etc, etc.
here in the Comox Valley, we have a particularly well loved and extremely fun trail known as Thirsty Beaver (upper and lower). it's one of these trails that can get trashed readily by overuse especially if wet. the builders actually requested that people avoid it in a posting during the first winter.
the recent adventure race MOMAR just sent some massive amt of riders through there last weekend during the mtn bike leg.
i wish race organizers would think of these things and avoid these trails, especially given the time of year and likelihood of wet trails. have some respect for the builders and locals.