I have to ask if you have an understanding of how Mavericks handles memory management. OSX does not "take up more than 4GB on idle." As already stated in this thread, OSX uses available memory, it does not mean memory is not available. If you have a 4GB model, it will show most of the 4GB being used, if you have an 8GB model, it will show over 6GB being used. Mavericks manages memory differently.
God knows what 4GB Macs are like and so do I since I have one. It flies. I can have 10 browser tabs open, with iMovie, iMessage, Word, Excel, Spotify all running simeltaneously and my memory pressure is still COMFORTABLY in the green. I am not a power user. I do not do heavy video or photo editing, I don't run VM's or anything like that. I use my computer primarily for college (writing papers, working on spreadsheets, research), light photo editing and occasional video editing for family projects and such, surfing the web, listening to music etc.
There are millions of users who use their computer exactly like I do and for that, the 4GB base model is more than enough.
Would the base model work for you or many other users? It all depends on what you do with your machine. Many users do need 8,16 or even more ram depending on their habits, but many do not.
I would agree that it would not be a bad idea for the OP to go ahead and get a 16GB model due to his usage and such, but to make a blanket statement that you would recommend a minimum of 16gigs of ram for all users makes no sense. Why would I possibly need 16GB of ram for my usage when I am not even close to pushing a 4GB machine? Why encourage someone to spend hundreds of dollars more on something they will most likely never use.
I understand many people feel the need to future proof their machine and to an extent I can understand that. However many users purchase way more machine than they need. By the time they get to a point(if ever) that they actually need all of that ram or that i7, the machine is 5 plus years old and other components start breaking down which still results in failed attempt at future proofing.