Did you know there have been many generic top level domains released since .com .net and .org? For example, .biz, .info, .name, .mobi, and .asia have all been relatively recent. Can you understand why many people would compare the success of these top level domains to the potential of .co?
Moreover, if it's not possible to make any comparisons to .co given the rapidly changing interface of our marketing world, then why have this thread at all? Your claim is that that evidence is completely irrelevant, and there is no argument anyone can make that can be substantiated. If this is the case, how are we supposed to engage in a conversation with any sort of intelligent speculation? It's as though you're asking a question, and then sticking your fingers in your ears and yelling "la la la, can't hear you" like a child.