I think it comes down to a matter of taste. Having the ability to restrain one's ego is the mark of a true professional. If you're good, you don't have to flaunt it, your work just speaks for itself. For startups, this doesn't mean you can't promote or sell your product as you see fit, but you shouldn't run around saying "what we've come up with is the most brilliant thing in the world." A lot of people do this and it's quite the detractor. Again, though, this is a taste thing and not a universal preference.