I dont think its unusual for linux to use pretty much all RAM, I think
this is just how linux/Unix memory management works.
You only need to be concerned if your machine is starting to require
lots of swap.
Sorry, but this isn't true. All programs should release memory at least
when they exit and better still as they no longer require it. A failure
to do so just bad programming. It's nothing to do with the operating
system (unless some part of the operating system is written in this
way). You can check what processes are using memory with