As the conversation seems to have veered back away from flaming and Apple-bootlicking, I'm game to try and participate again.
I think you answered my question. By geographically independent I meant if both the machive with the server on it and the iPhone are on the same network, which is not the home network (for example in a hotel). If I get you right, having configured the server to work on my home network with the IPs I can fix for each on my router, it will have to be reconfigured for a third party network where I am unable to decide IP addresses as they are given by the system DHCP.
I travel a lot. A LOT. Thousands of hours a year, internationally, in my job as an airline pilot based in the Middle East. So I have set up in thousands of hotel rooms over the years, in hundreds of countries. Not to mention public WI-fi in hotels, coffee shops, airports, on and on. My travel gear includes an iPhone, iPad, and 15" MB Pro Retina, and Airport Express to tie it all together. These are some of my observations.
Internet connectivity is a relative thing. Speed and access vary wildly, from non-existent to blazingly fast to at times government-blocked (becoming more common). At times access is throttled and blocked even at the local level, by the hotel, or by the ISP. Ports can be selectively blocked, VPN's don't always work, bandwidth caps are imposed, and the like. It isn't a given you will able to blithely sync your devices over the internet. Not a problem if you are in the US with fast broadband and never venture more than a few miles from your home.
More and more hotels have only wireless access, with less and less Ethernet in the rooms, so the Express can't create a local hotspot with internet connectivity. Even with wired access, many hotel systems are now configured to prevent you from creating a subnet in your room (can only use the Express as a Bridge, ie with one device). Wirelessly, most policies will only allow access to one device per package purchased (tied to your hardware MAC address).
Point in all this? For the professional business traveler, Cloud sync isn't just a nuisance or philosophical objection. It's something inconsistent enough to be unusable. Sorry, but I can't wait until I get back home in a week to make my devices match. And none of this even begins to touch the privacy issues. My buddy snowdrop or whatever stated that things are moving more towards a wireless world. Perhaps. But the world is also in a post-Edward Snowden, NSA scandal, Wikileaks world, and teeming masses of tech-illiterate i-Lemming cabin crew girls aside, people are becoming more aware that their data is their identity and one of their most valuable possessions. Which is why Apple, Google, and the guv'mint want it as easily as possible. Not paranoid, just the reality.
At this point I'm sitting tight in Mountain Lion and thankful that the awful experience of upgrading to iOS 7 acted as a warning to prevent me from jumping right into Mavericks. I'm toying with the idea of going the server route for local sync if I do go to Mavericks but will be waiting for a good long while to see what others more clever than I come up with to work around Apple's unilateral policy. I'm definitely considering any hardware and software vendor outside of Apple for longterm solutions. It's not being petulant, I have no choice.
As far as the technical niceties of a local server solution, I've administrated Linux servers but not OS X, so I'm not totally conversant on what it can and can't do. I'm hoping that it utilizes Bonjour for local networking, it would be a pain to have to switch back and forth from static to dynamic IP's just to sync calendars and contacts.
I used to mock the Windows camp for having to spend hours kludging their systems just to get them to do basic things possible on my Mac. No more.