In the 3.5 cycle, we introduced zipped p2 repositories in the build. These zips could be used to provision your target platform or update your install. We left the per-platform zips on the download page for Galileo. With 15 platforms multiplied by several permutations of features, and runtime versus source downloads, these zips consumed significant space on eclipse.org and the mirrors. Not to mention the fact that platforms other than Windows, Linux and Mac have very low download numbers.
For Helios, I’ve replaced all the platform specific RCP, JDT, PDE, CVS, examples and releng tools zips with p2 repositories specific to that feature. For instance, instead of 15 platform specific runtime RCP zips, there’s a p2 source and runtime feature for each one. The SDK and Platform feature zips for each os.ws.arch combination continue to be built.
More information
How to Consume zipped repositories.
bug 280622
Built to Run 
If anyone's wondering how to convert from the new repo format back to the old-school runnable format, see Repo2Runnable. I've attached both Ant and Bash sample code there.
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