Not sure how they play this out in the future but for IDEA 12 vs latest PyCharm they first added the new python-related features to PyCharm and then to IDEA python plugin. The codebase seems to be the same but release cycles differ.

Also some of the plugins are available only for PyCharm but this will hopefully change (for example, Lua plugin is only for PyCharm).

As of today I haven't found a way to add new packages to virtualenvs in IDEA but they are easy to install in PyCharm.