Push, pull, shove
You ask at the end why a person would want to maintain an identical set of contacts on four macs and two iPhones, simple, he needs his contacts sync'd so that which ever machine he sits at always has the latest info.
I have the same issue at home in that my wife and I have macs, we both have iPhones and there's a couple of PCs around the house too. My wife uses her Mac Book usually when working from home, but also, for large spreadsheets, etc. she prefers my iMac. I run a lot of VMs, etc. which means I'm often on one of the PCs.
The point is, when I pick up a skype phone, or my mobile, I want to just see the contacts there, not worry which device I've picked up.
This is why I will be putting Exchange back in (small business server) as this gives me my bookmarks, email, everything, on any device I happen to have to hand.