Hmm, seeing as Push seems to work between iPhone and MobileMe, I have other ideas as to what is happening between MobileMe and Mac.
From what I've read, apparently this is the conclusion:
MobileMe -> Mac (Push)
Mac -> MobileMe (Sync)
I have played around with it and I think that MobileMe -> Mac is infact 'Sync'. Let me explain. Under the MobileMe options in System Preferences, we obviously have all selected to Sync automatically. We have just found out that this "automatically" actually means every 15 minutes.
So, if the Mac is Syncing every 15 minutes with MobileMe, then really, it could be doing something like this:
I'll start with 9am for symplicity:
9:00am (Mac syncs with MobileMe)
9:15am (Mac syncs with MobileMe)
:
9:45am (Mac syncs with MobileMe)
etc...
Now, say you change a contact on MobileMe at 9:01am, technically that contact will not be changed on your Mac until the next Sync time, which is 9:15am, approximately 14 minutes later.
Now, say you change a contact on MobileMe at 9:14am, again, that contact should not be changed on your Mac until the next Sync time, which is still 9:15am, which now is only 1 minute later!
From the article posted in the first post from Apple, I do believe MobileMe -> Mac and Mac -> MobileMe are both Sync.
The disagreements on how long its taking to Sync (and thoughts that it may actually be Push) can only be what I have just explained in my opinion.
I may be wrong, but that is what I strongly think is happening here.
EDIT: I should state that I still think this is absolutely unfair Apple has done this.