Handhelds will always have a sales advantage and can easily outsell consoles because of four reasons.
1. They're generally cheaper. This makes it easier for people to buy one or more handhelds.
2.Siblings. If your brother wants to play a game with you on a console, he just grabs a controller and you play Madden, Mario Kart or whatever. Try that with a handheld. It's very common for families to have two or more of the same handheld system. And it's easier for families to do that for the reason listed in #1- price.
3. Limited space. Look at two of the current consoles, especially the PS3 and they're huge. A lot of people don't have the space for more than one of these consoles unless they really redesign their space. A handheld can fit in your sock drawer or just about anywhere in your house.
4. Handhelds make for good time wasters, whether it's commuting to work or school by public transportation or a break, lunch, recess, etc at work and school. Again, you can't realistically do that with a console. And many people who think gaming is geeky or for nerds and wouldn't be caught dead playing video games don't view handhelds in the same way and have no problem buying one to waste time when they're bored or have spare time. A big reason that Tetris has always been so popular and also helped the original Gameboy take off in sales.
I'll come up with something better eventually...
