I agree with all the comments here. I can't believe Apple took this feature away without even flagging it. I just submitted feedback as WendyRobin suggested.
I often fly internationally and do much of my work on the plane, where there is no connectivity (yet). Being able to add/change/delete/edit items on my calendars and contacts on my MacBook and sync them directly to my iPhone is crucial, as it allows me to be ready to use that info from my iPhone as soon as I land.
Now my alternatives are:
1. Go back to Mountain Lion (probably my best option);
3. Enter everything directly on the iPhone while in flight (I don't think so);
4. Look for WiFi as soon as I land (often not so simple), connect both my devices at the airport (expensive) and then wait for them to sync (wasting time).
5. Use the Export/Import method for the entire Calendar and Contacts files (pain in the a**, plus huge potential for corruption when repeated often).