Isn't it true? Marketing strategy?

That a business, whether it be the gaming industry or the technology industry, leave certain things out of their products to add later to their next generation of products? For example, take the Ipod Touch. It doesn't have a camera yet, but has a bunch of cool neat features. The only thing that is missing is a camera. Now I say that the reason why they leave this feature out is to add it later to their next gen, you know to keep the consumers excited, is it tue? Is it a good marketing strategy to leave certain features out to keep the fans happy later and later on? Please provide link to these actions.