The fact that lawyers and owners of companies in the business were making statements of legality about OSRIC (casting doubt) is seriously unethical (and possibly illegal). Chanault's attorney (and wife) should have warned him not to make such doubts publicly known. A judge could see a "response to a question" by such a person as a means to an end (a smear campaign). The fact that OSRIC was designed to be used by 3rd party publishers and that TLG would be in direct competition with these 3rd parties would likely be relevant in such a case.
It is not unethical or illegal for people to state an opinion based on case law and their own legal knowledge about a third party, even if they are in the industry. I suggest you read up about legal ethics and libel law.
You seem to be saying that anybody who makes a statement regarding legality of OSRIC (usually in response to a pointed question like "why don't you support OSRIC"), if they have a competitive game should STFU. I don't think that's right. Note that neither company is doing things like accusing them of illegality, they are simply stating that they think its risky.
In any event, the last thing WOTC would want to do is bring this to court and clarify the law in a way that was not to their favor. The impact could be massive (possibly hurting all of Hasbro its parent company). The most likely scenario would be for WOTC to offer OSRIC's owner(s) cash to make it disappear (and for all I know they have and it was turned down).
But then there is a risk of WoTC winning and setting legal precendent that would threaten a lot of the clones.
The threat of a lawsuit is big enough to make people risk adverse. I think C&C was developed very carefully because, while Gary wasn't directly involved in its creation, he was going to release Castle Zagyg through that game system. EGG was a target before. Take a look at this lawsuit.
http://www.darkshire.net/jhkim/rpg/copyright/cases/tsr_vs_gdw2.txt
Now, Dangerous Journeys was VERY different from AD&D. But look at that discovery line-list. Mr. Gygax had stated they could have probably won the case, but all the parties couldn't afford it. So they settled. A game was destroyed, GDW likely suffered from the results (which might have contributed to their eventual shutdown--not sure exactly), and even TSR accrued some debt to the lawyers. (I suspect they more or less feared EGG working for the competition--while that was unlikely to happen with the WoTC of the early 3e days, you can never trust that a company won't change).
This is the type of risk involved. Each company has to evaluate risk and make their choices. Answering questions honestly is part of that.