Few corrections there.
First, you'd be surprised what you can get out of an ARM with some well thought out code. I've been using ARM chips since the early 90s and they're fantastic little power houses with tiny power requirements. Love 'em.
Anyway, I believe all the references to iPods will have been to the iPod touch, which is an Samsung ARM running between 400-600MHz depending on the generation. They have fixed pipeline GPUs similar to geforce 2-3(ish) spec. Whilst this couldn't run the current PC Audiosurf it could run an optimised port without issue.
PSP is a custom MIPS-based CPU with a second MIPS CPU for "media" and a seperate GPU as well, running up to 333MHz, it could manage Audiosurf with ease at its resolution. Comparing raw power to the PS2 is a bit unfair on both devices as they work very differently internally although the actual graphics produced on screen are similar.
DS would struggle. The DSi has more of a chance (faster CPU) with SD card support it makes more sense as well, but I'm unsure if it's possible to target just the DSi from carts at this point in time. I have a suspicion Nintendo will be bringing out a new hand-held either this year or next anyway.
The Wii from a CPU/GPU perspective is just a faster gamecube. Nintendo did this to stay in the console market. See, the GC hardware was costing Nintendo very little to put together, so adding just a few expensive parts and dialling up the clock speeds a little allowed the overall cost of the Wii to remain low for Nintendo, so even if the console itself did as badly as the GC had then Nintendo would still make enough to chug over another generation. As it turned out the Wii has been very successful, which means Nintendo are laughing all the way to the bank. But the GC could manage Audiosurf anyway, so no problem on the Wii.
X-Box 360 isn't PC based. It's PowerPC based (that is the old Mac CPUs, not x86), so technically are the Wii and PS3, although the PS3 has an array of Cell processing units in addition to the PPC core, anyway both 360 and PS3 easily have the hardware to cope.

But as has been pointed out many times, it's all a bit pointless speculating at this stage since Audiosurf uses Quest3D and that is very much Windows only.
Just as a last note, I'm basing the "what can run" on Normal/Enhanced for most of these and Minimal in the case of the DSi. Take a look at the Zune version as a clue:
http://www.youtube.com/watch?v=63qaVvV0pVw