The choice of computer to run on the TurtleBot is a tradeoff of battery life for computation and price. In general more computation is better. However also in general longer battery life is better.
The choice of the dual core Atom processor in the Asus 1215N for the default processor provides enough processing to do all of the navigation stack and process the Kinect while leaving most of one core available for the user to develop their own functionality.
If you go up to an i7 or other more powerful CPU you can do more processing, but you need to be careful about what you're expected battery life is.
The same goes for the RAM though it's less power hungry.
It is definitely possibly to use the graphics card for certain applications. Right now the graphics card is most heavily utilized by visualization and simulation libraries which are not especially useful on the TurtleBot laptop. However there are CUDA bindings in the works for both PCL and OpenCV which could offload a lot of computatoin to the GPU soon. In Lucid the EeePC's Optimus technology is not supported, but I have heard of drivers working on Natty.
Using the EeePC is also a price optimization. The EeePC is in a highly competitive product space with many similar models from multiple manufacturers making computers with almost exactly the same specifications.
Did you ever build a souped-up turtlebot? I just installed a Mini-ITX mobo, low power i5 processor, and ssd in the cargo bay. Maybe I'll post some benchmarks
@patrick_hammer How does your solution work? How do you power the mini ITX board? Maybe you can post some more details on your project.