Keep in mind they are talking about all sales in general not just people who are buying them for themselves.
Gaming consoles especially new released ones are great for marketing and will be often used as prizes in stores/arcades/bars/schools/etc. As well as by radio stations, small businesses, numerous companies offer prizes off sites like twitter for them. Some companies also simply offer them as entertainment they often have a few up at places like Dave and Busters sometimes in fast food restaurants like McDonalds.. events that have parents with kids sometimes get them to keep the kids busy. Some jobs that have downtime allow the workers to buy them for example a friend of mine is a firefighter and they all chipped in to buy a PS3 and 360 at the firehouse. And of course not to mention a surprising amount of people manage to stupidly break their consoles.
I still think it's unlikely they will hit that billion mark but I don't think it's all that farfetched.