Ok, so you're saying that it makes sense to risk frying a $500 laptop instead of a $25 Pi? Riiiight.
Only an idiot would connect something capable of damaging their computer directly to it. This is what opto-isolators are for.
And when you say "underpowered", that's because you hadn't realised that the SoC was designed to go into hi-def PVRs or BluRay players, so it has a muscular GPU, and the "underpowered" ARM CPU was an afterthought...and you haven't kept up with the news,
You're making an incorrect assumption. I say the Raspberry Pi is underpowered because there are similar SoCs available that have ARM Cortex A8 or A9 CPUs in them which are clocked higher than the older ARM1176JZF-S CPU in the Pi and which support the newer ARMv7 architecture versus the Pi's ARMv6. This is a big deal since ARMv7 CPUs can run at their full potential using standard armhf Linux distributions.
Also, the GPU in the Pi isn't as powerful as the Raspberry Pi Foundation would have people believe. Just look at the results Luc Verhaegen has achieved with the supposedly much weaker GPU in the Allwinner A10.