Which is all well and good, if you assume the market is a fixed size, but it's clearly not. It's massively grown.
In its lifetime, the Game Boy (and Color) sold nearly 120 million units. Over 12 years. In the three years the GBA existed, it sold 80 million units. The DS has sold 150 million in 7 years. During which time the internet has happily coexisted with it.
As I already said in this thread, those sales largely predate the rise of the smart phones and app stores.
The DS was huge because it also catered to a new audience, in particular older people and women. It was because of games like Brain Training and Sudoku, which you can now get on smart devices.
When I bought my DS when I used to commute it was before the iPod Touch was released, which had no games at the time anyway because there was no app store.
The market has changed significantly. The most desired products are smart phones and tablets, and as another poster already pointed out, this is what you see people using now.
I'm not saying the Vita doesn't have a place, I just think it won't be quite as successful as they are hoping. If anything I think it's going to end up largely being sold to the 'original' market which is kids and teens.