You might be right. But I think if they had announced this as a stretch goal would have been even more publicity resulting in more money.Isn't it already though? I'm not convinced that individual stretch goals actually do much to sell a game; they're all about the publicity. This one is bound to bring more notice.
I guess the main reason they didn't do it is that the whole campaign including the stretch goals had been worked out in detail before and they didn't want to change that plan.