How to create /usr/texbin?

You can easily change the path for the TeX programs also with TeXShop and TeXworks; just make them point to /usr/local/texlive/2013/bin/x86_64-darwin; the drawback is that you need to change this at every installation. MacTeX does this for you by creating an infrastructure in /Library/TeX and making a symbolic link /usr/texbin that's managed by the installer or by the TeX distribution pane in the System Preferences.

If you don't want to download MacTeX and prefer to directly install TeX Live, you can create the symbolic link yourself by

sudo ln -s /usr/local/texlive/2013/bin/x86_64-darwin /usr/texbin

(change x86_64-darwin to universal-darwin if you don't have a 64 bit system); just remember to do

sudo rm /usr/texbin

as soon as you install a new release, before creating the symbolic link again.