Figured I'd try it out, but yeah, I get the impression that, with Siri, it recognizes and understands how to interpret a lot of different phrases and wordings. With S Voice, it seems like you have to give really specific commands in order for it to work. For instance, I tried something simple like "Where can I get something to eat", and it said it didn't understand what I meant.
I dunno, personally, I find stuff like Siri silly, anyway. Why would I want to sit there talking to my phone, when I can just as easily do what I want with a little finger work?