Hi all,
I have learned (thanks to the el-get developers) that org-mode uses with-eval-after-load, which was added in Emacs 24.4. (See discussion [1].)
I confirmed that the master branch of org-mode loads (via el-get) successfully in 24.4.1 and fails to load in 24.3.1.
I'm not sure what the compatibility policy is in this project, and whether or not this deserves a fix. I personally can work around this by building Emacs from source on older machines, but I will need to do this on every Ubuntu 14.04 machine I use.