Sure, people argue on the semantics of IP infringement and while many feel that intellectual property laws are woefully one sided, most of what I've seen suggests that at least a fair number of people feel that copying material in contrary to the creator's wishes is wrong. Do some folks do it anyway? No doubt. Regardless, I think much of the hard assedness has been in response to the media companies and lawmaker's approaches in addressing the issue--- poor legislation that overreaches, failure to address the actual issues that leads to piracy, copyright length extension, circumvention provisions & fair use implications, etc. In the end, I can be against efforts like SOPA while also being against ip infringement. Similarly, I would assert that it is not inconsistent to feel that curebit's approach to publicly using another other company's design w/o permission directly in their commercial product is unfortunate while also feeling like IP in the US needs to be retooled.
Ultimately though, this forum compromises many viewpoints. While there will be trends, consistency when dealing with large numbers of folks seems unrealistic (but again, I don't think having issues with contemporary IP law and being against using another site's design in a commercial product demonstrates a consistency issue. It's more of a "dude, not cool" thing to me.).
In regard to the lack of detriment, certainly at least one representative of 37Signals is unhappy with it. If it were my design, I'd prefer that my efforts remain tied solely to my products given the time and money spent on them since I think there is marketing and branding value in developing a reasonably unique look and feel even if the products themselves are not direct competitors. Do I recognize that designs will inspire other designs? Certainly. The line between a copied design and inspired one is blurry. Would I personally give more leeway to someone who was just experimenting for a non-commercial, personal project? Probably. This, however, was a commercial entity that just received a big check for their (and 37signals') efforts. That said, if I were an employee of curebit, I'd probably have felt uncomfortable with the approach they took regardless of any legal implications that may exist. It would just kinda feel wrong, ya know?
Anyway, my initial reaction was along the lines of "well, that was stupid of them" and progressed to "WTF is wrong with this guy?" due to Allan's tweets in response to dhh. Some of his tweets have almost felt like he was trolling for controversy/publicity. Regardless, I really think he should simply stop tweeting at this point and let further public responses come from someone better equipped to NOT dig themselves deeper.