Stop looking at RAM consumption numbers on processes and look at swap used, and also the new "memory pressure" graph.
OS X, like any modern operating system designed since the 1990s, will use RAM for cache unless it is required elsewhere.
Mavericks, in contrast to previous versions, will also compress memory as required to fit more into RAM.
How much ram kernel_task appears to be using is entirely irrelevant to determining whether or not your mac is under memory pressure.
read this:
http://arstechnica.com/apple/2013/10/os-x-10-9/12/#energy-saving
yes, it is long. but it goes into great detail about how and why Mavericks uses memory more efficiently and can run a lot more in memory than any previous version before it hits swap.
cliffnotes: on a 16GB machine, the author was able to run 24 GB worth of applications before the machine started to touch swap at all.