john, the other big factor is the accumulation of dirt, body oils, sunscreen etc that clogs up stuff in breathable rain gear. The abrasion aspect is a factor, my rain pants were still beading in some areas, but not in the areas that were clearly getting rubbed and or contact with my elbows when sitting etc.
Washing gently, then doing the dwr reapply really truly made a huge difference. A bottle of dwr stuff and using a simple mist spray bottle , but following the instructions (spray the stuff on when item is still wet) is totally worth it for any rain jacket I would say, and totally worth it money wise over the long run, especially if one has numerous rain gear garments in your household.
I know I'm repeating here, but I finally realized the importance of washing your rain gear once in a while and reapplying the dwr stuff. It will last longer and work better too, a win win for anyone.
If I recall, its not good to use regular clothes detergent, something in it not good, clogs up the pores or something, but easy to read up on.
For sure washing is important but the thing that I found most interesting was point # 5 - you can revitalize DWR with 30 minutes in the dryer. That can certainly prove helpful to someone in the middle of a big trip and struggling with their Gore-Tex in the rain.
Regarding washing, I used to use the Gore-Tex specific detergents but I'm currently experimenting with simply using less regular detergent.