I asked the moderators by clicking the "report" link on the first post. They sent the following and said it was OK to pass the info along

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The response is Gravity hobby.com was added to our language filters because they choose to ignore RCU''s rules for commercial posting in our forums. Even after numerous warnings they continued to not only spam our forums, but they also created shill accounts in order to create bogus threads in order to advertise their products.

RCU has rules in place that allows businesses like this to make posts in our forums to get the word out about their product. However, they choose to ignore those avenues and instead decided to flood our forums. Our only avenue to combat this was to add the website address to our language filters.
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So, no great political conspiracy. No oppression of "free speech." Just an attempt to block a spammer.