I was not referring to any RAM manual, but your Macbook Pro manual. Since I do not have the latest one I can only reference mine and all the manuals for the three MBPs that I have give instructions on RAM replacement which indicates that it does NOT void the warranty (200, 2010, 2011) but only on the RAM. If in the process of swapping the RAM you damage the MBP, then that damage will not be covered by the warranty.
I too have 16 GB RAM in the 2011 MBP so that gives me bragging rights, but the important point is that the cost was about $90. A couple of years ago the cost would have been over $1000. Since it is very rare that I use more than 8 GB RAM, an increase would have been fiscally unsound two years ago, but at current prices the increase can be justified far more easily.
Based on what Clinton has described over time, his MBP installation looks like an octopus with the various paraphernalia attached to it. 'Normal' users might have one or two items attached (I usually have none) which suggests that there would be less demands on the MBP. If one chooses to keep many applications open, then additional RAM can be useful, but note that is under the users control.
Ciao.
Clinton, regarding the 'average user', you can take it any way you want to, I simply will keep that point confidential. đ
Best regards.