As long as Google thinks about its users, publishers and advertisers. Google will always stay. As long as they don't monopolise the internet industry on their own. And i don't think it requires to have a new domain for any new product they launch, this is just a branding strategy that is common. Companies just want to be known, to stick to people's head that they are using this kind of Brand.
1. I think that this strategy is faulty; 2. Think Microsoft, think Windows XP. Think Google, think Search Engine. It's not such a successful branding if you don't think Gmail or Windows 2003 EE.