It's interesting how people compare Apple's sales of different categories to its competitors single category.
Sure, if you spent all your time on Twitter and Facebook and you like 4" keyboards it's great.
The only interesting comparison here would be between tablet and notebook sales, because they are the only 2 markets that somewhat overlap.
How many people do you know who own an iPhone and don't have a computer as well? Saying that people buy new computers less often because they spend some of that money on smartphones could make sense, but saying smartphones are taking over sounds kinda silly.
The trend may be even more important than the absolute numbers.