Yes, ReWire is a standard (like VSTs) that's been around for over 10+ years now:
en.wikipedia.org
I think that the reason that Serato chose to make a proprietary link between Ableton Live and ITCH (and SSL) is because they wanted the the audio integration AS WELL AS the UI integration (which ReWire doesn't do).
Time will tell if the Bridge is a compelling feature. I wish that ReWire was supported instead - that way I could use ANY ReWire slave - including Ableton Live - instead of JUST Ableton Live. Hell, we could've used ReWire to sync to VirtualDJ to get video!
But that doesn't mean that the Bridge is bad. It's just proprietary to Ableton Live... which isn't free. At all.
-KLH