I think it's relatively simple.
LinuxMCE is designed to be a consumer level all-in-one solution. So connect it as the wiki suggests to your router and it will work (mainly, once you've twiddled with it a bit). for most people this is all that you will need.
There are other people, who have specific requirements, and specific knowledge, that may use it in other non-supported (as much as anything is around here) ways. Personally I have a problem with any one element being a single point of failure, as I have a problem with essential systems relying on computers/servers. So what I have is a series of self-contained systems that work without any requirement for server level control. I have a self contained heating control system, a knx based electrical and intrusion detection system (door sensors and PIR's), a 1-wire sensing system, a separate asterisk server integrated with POTS. I have quad LNB's on my satellite dishes so that they can run a setop box as well as DVB-S2 tuners in LinuxMCE. I have purchased other items (like my Onkyo receiver) so that they give me what I want as a stand alone unit, as well as being capable of being integrated into LinuxMCE. I have put together these items, and planned the construction and layout of my house in such a way that everything works without LinuxMCE, but can do more and work better with it. I have not placed all my eggs in one basket - for example my heating control system has an integrated webserver with the capability for remote control, but I have also wired so that I could replace the thermostats, timers, and valves with KNX units if I later choose to go down that route. I also have allowed for z-wave capability if KNX doesn't meet all of my needs. I have a lot of spare power and CAT6 dotted around the place. I have TV aerials, radio aerials (dab and FM) as well as my eight satellite feeds (from two separate dishes, one motorised). I'm just not the sort of person to rely on one critical system working.
In addition to my LinuxMCE network I have a need for a work network (I work from home and integrate using vps with a number of sites that I administer from an IT perspective). The scope of LinuxMCE just does not meet my needs in this area. So my intention is to split LinuxMCE and my work network using VLANS over a Level2 smart switch (I've been working on that today, actually). My router will connect to both subnets (work and LinuxMCE) but LinuxMCE will totally control, as designed, the home subnet.
I need it to work this way. I may very well get shouted at here, and I expect it to require a lot of time and effort on my part to get it working, but then this is a long slow project for me and I accept that.
So that's where you need to be. You either need to use the system as designed and take recommendations on equipment that it is known works well with LinuxMCE (something that I have found difficult to achieve in Europe when most of the available advice doesn't always apply as well), or you need to define your own requirements and be prepared to do your own legwork to get it working.
LinuxMCE is a marvelous piece of work almost without peer. That does not mean that I agree with all design decisions, nor with what is well supported and what is poorly integrated or supported. The framework is there to make it something special though, and I'm going to have a crack at making it work for me.
If you really want an easy push to play system, then you need to speak to one of the system integrators and buy an off the shelf system. If you want to do something against that intended usage of the developers you have to accept that you are on your own - they're stretched enough as it is. Having said that, I believe that LinuxMCE can integrate with my requirements for a system, and my needs are outside the intended scope of LinuxMCE as designed.