The same can be said about phones and portable video game systems. It's all ARM CPUs with Imagine GPUs. Android, iOS, Windows Phone 7, Blackberry, webOS, Nintendo GBA/DS/3DS, Sony Vita all use the exact same chips from the same design firms.
The big hardware differentiator is what cost/performance balance you want to strike. Newer architectures with newer manufacturing processes cost more plain and simple. And there is a spectrum of other off the shelf components to round out the package.
There can be some play in getting more out of a design with engineering tricks or getting better components at the same cost with economies of scale. Or you can corner the market by buying out the entire manufacturing capacity of the best components to deny your competitors (or vice versa). But it's pretty much you get what you pay for.
Nintendo builds hardware two to three generations behind to save a lot on costs. Not because it doesn't know how to get something faster and better. The upcoming Wii U is basically an older PowerPC CPU with an older ATI GPU. If Nintendo wanted, it could create a crazy powerful console with a $1000 CPU and dual $600 GPUs that nobody would buy. All it needed to do was tell IBM and ATI what it wanted. It wasn't a matter of engineering that steered them away, but a matter of economics. Which if you remember right worked great in the short term for the Wii. But as everyone already knew wasn't a long term play. Hence the earlier-than-everyone-else release of the Wii U.