But there's no way to make sure you all start at the same time. You have to manually make that sort of happen, and you'll never really be perfectly synced up (and it'll be even harder on the PS3, where there's not even voice chat). I don't understand why they couldn't have simply included an option to really go head-to-head.
I think the answer is lag and mainly rewind. They want you to compete and if you smash your friend, how would he rewind? Take even the puncher back in time? Forever and ever?
On ps3 you can send message so some people they will join you in your custom global event and then they will see when you jump out so they can too. Sure, not head to head, but on same slope, with same conditions and rewinds that wont affect anyone else. Scores and times matter.