PC and Mac have the same underlying hardware tech, but their software and marketing are what differentiate them.
In my view...
Hardware-wise, Arc suffers from the "me too" or better mouse trap issue. Sony is also pushing quite a few pieces (Arc controller, 3D, any chargeable PSN plan). They will need to think the hardest to figure out what exactly they are pitching (combined). Relying on their hardware marketing guys alone will likely fall flat (Think PSP Go, and earlier piecemeal PS3 marketing). Sadly, they only hold a partial picture of the final product.
Software-wise, if they can put more new ideas like the sketch recognition stuff to daily use, then it would appeal more to the end users. The overall software experience (e.g., Minority Report's controller-free UI, or Harry Porter style magical wand) will depend on how well they work, and how useful they are. In general, they both allow controller-free applications, but choosing the best tool for the job would be key in the long run. At this point, I think the no-remote pitch is great for home theater. OTOH, Arc has no signature software yet, except for WiiSports. So again, Sony needs to look for its own flagship software different from WiiSports (Preferably, serving a different need).
I'm curious how Sony will sell this as innovation and new technology, like the SIXAXIS at E3
SIXAXIS is great except that Sony didn't go far enough (No commitment => Didn't think through enough). Folklore and Flower justified for the existence of SIXAXIS. If they take the current hardware centric approach, then Arc will definitely suffer. So this time, hopefully they go deep.
The above are known issues and perception of SCE. Arc is more interesting to me as a way to see how Sony executes (and improves itself -- more than just talks). From the GT5 thread, I _think_ I can see marketing fighting/patching with the dev since they come in so late (You hear Kazunori say, "It's up to marketing now". Ideally a large part of it should happen at the beginning, not at the end).
Argh, that Smallville video is bad. The actor's action doesn't match up with the game
at all.