All functionality from the mentioned products would be available through IntelliJ IDEA plugins, however some features (really few non-essential) may be temporarily unavailable due to newer or older versions of the IntelliJ Platform. It is worth noting that the plug-ins are not sim-shipped though, so there is some delay.
Let me address now your specific situation as described above.
IntelliJ IDEA 13 will be released very soon. It will include the features from the recently released "smaller IDEs." Another point is that you do not need WebStorm. All WebStorm features are available in PyCharm and RubyMine or can be installed as plugins. Again, the plugins are not sim-shipped and will be available sometime after IntelliJ IDEA release.
To recap: IntelliJ + plugins cover all functionality that all our IDEs provide. On the other hand, dedicated IDEs are convenient being more lightweight, offering a simpler UI and faster performance.