Catching up to the plot? EAS was proprietary and worse, paid!
Perhaps I'm ignorant, but in my six years of using smartphones (T-Mobile/HTC G1, Nexus One, iPhone 4, Lumia 610, Galaxy Nexus, L920 & Nexus 4) I've never used anything but the built-in calendar/contacts apps. I've come across apps that are basically a front-end to the existing databases, but the actual sync mechanism has been baked into the OS. Now, iOS has support for calDAV, WP will soon have it as well. Likewise BB et al. Android is the only OS that includes both the Google calendar API, but DAV works just as well (on iOS at least). My perspective is that as long as the OS sync mechanisms work, there's nothing to worry about. Of course, if there are widely used third-party calendar apps, please let me know.
Remember that apps can still read/write to the phone calendar and this syncs using whatever the protocol is. For example, TripIT. I enter a flight number and date; TripIT then creates appropriate calendar entries for me. This will still be possible because TripIT doesn't care if my phone is using EAS, DAV or gCal.