I love the site as well, and hold Bink responsible. He said that he was really enjoying making the site, and Easter eggs like these prove it.
As for the sludge, it just does...
Although the obvious reason is that kids know that radioactive waste is dangerous, the worst it could probably do is wreck their paint-jobs, unless the sludge could heat up as it decays, which would damage robots through extreme heat.
Alternatively, the power core of robots could quite likely be a mini nuclear reactor (especially with Heroes), where if the unstable radioactive sludge were to come in contact with the core fuel, it could cause a meltdown of the core, blowing up the robot. (This might be a bit violent... )