I could not say how much Apple gives back I just know I've seen the program mentioned on their web site. I personally have never had to do a trade in as I've never had a battery failure or even a battery reduced by much off the full charge.
In regards to charging there is no app that I am aware of, but I've not really looked either. There are several battery applications though, so one of them may have this feature. I know how I would do it, which is just to set it to charge and when it got to what I think is about 60% I'd stop charging it. It isnt' rocket science and doesn't have to be EXACTLY 60%. Just some where in that range.
Well your friends aren't to swift if they are struggling with their batteries and lack of a slot, because they should have known when they bought them what they were buying. Apple can't be held responsible for uneducated buyers. When I purchased my iPod Touch and iPhone I considered my library and how much space I would need, then bought accordingly. Not to mention with the auto fill up feature in iTunes I can get my music swapped out pretty often and this keeps it fresh.
Once again I don't know of any reason whatsoever I'd need a slot or a 2nd battery.. None, Nada!! Also there is nothing wrong with iTunes I think all that stuff that people get into about it is just BS in most cases. Most users never have problems with iTunes and it does the job for the iPhones, iPod's etc. There is 3rd party software that will let you do basic management if that is all you are after, so that is a non issue.
Just seems to me you are looking for stuff that you perceive as being its weakness to say "OH yeah that is why I won't own or buy one". "Oh yeah that is why I hate Apple", it's just seems so silly to me. LOL It is pretty clear that most folks know what Apple's iPod's, iPhones, iTunes are capable of or not, so it a matter of making an educated choice to buy one for yourself or not. I don't see where the complication is or where you complaint is. Apple doesn't support what you perceive as being so important! Personally I see why Apple goes the route they do because for most end users those things aren't important AT ALL! One thing you don't have a leg to stand on is that it clearly has not impacted their sales. These devices are not perfect, show me one that is. I could nitpick any electronic device and find things I think are shortcomings. But shame on me if I didn't do my home work before I made the purchase. If it was a gift and you just don't find any use for it due to those perceived issues, then donate it! I am sure someone here on the forum would love to have it.
Apple does what Apple does, so our response; we buy it or we don't!