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I have read some time ago that RedHat 6.2 is much more "stable" than 7.x. Perhaps it contains fewer projects in-development. So EDA vendors have chosen it as a "reference" platform. This does not mean in anyway that EDA software can not run in RedHat 7.x. At least I have tested some of them (S*nops*s, D#buss*, Tr@nsEDA) and found no problem.
IMO Red Hat Linux is a widely used distro and is constantly improving, but even the 7.2 release with all the latest upgrades has got a ways to go to be a top of the line stable EDA platform. Its generic technical abilities though are quite spectacular.