I think there are a lot of variables in this equation, but I do believe maturity of the provider is one of the key factors. I think the more mature providers have an SO of their own and out of habit of cleaning up at home, they clean up the client. Just speculation on my part as a lot of the young ones haven't been married or had/have a live in BF.
Here are other variables I've noticed. Location-- If it is her place, she will always clean me up. Never once have I gone to a lady's residence and she didn't clean me up or at least bring me a warm wash cloth. If it is my place, 9 times out of 10, it is self service b/c I know where the linens are. Hotel-- 50/50 on if she cleans me up or I clean myself.
Activities is another variable. If it is a slow, GFE type session, she is more likely to clean up. If it is a high energy/PSE environment, there is no clean up or at least any that I can remember other than me ripping off the cover in order to go again. Then there are times when we just lay there for 20 minutes talking and stuff, and then I finally realize the cover is still on. When this happens, I just usually clean up myself but on occasions, the lady has jumped up and done it for me.
Personally, I don't care. Sure, it is a nice touch but not really required. The best sessions are those when you really don't need a clean up as her mouth takes care of that problem. Nothing like a girl who swallows.