If someone asks a question on Stack Overflow about using Visual Studio, should Microsoft be able to delete it? Should they be able to sue SO? Should SO not be able to run ads for products that compete with VS?
But that's a red herring. The relevant complaint for this branch of the discussion is that GS wound up sponsoring a website that was clearly and evidently confusing to the public. They ran that site for commercial gain, and in multiple ways made appeals to 37signals for payment to gain more control over that site. None of that is kosher.
"To recover for trade dress infringement ... a plaintiff must prove by a preponderance of the evidence: (1) that its trade dress has obtained “secondary meaning” in the marketplace; (2) that the trade dress of the two competing products is confusingly similar; and (3) that the appropriated features of the trade dress are primarily nonfunctional."
Continuing ...
"Strength of ... trade dress depends upon the interplay of two elements, the uniqueness of the trade dress and the investment in imbuing a trade dress with secondary meaning."
... which makes trade dress difficult to prove, even to only a preponderance of the evidence.