Mine centers all around the MoBo. When I was building my current PC (my only build) I was having strange errors. I kept getting random restarts if I simply touched the case the wrong way. I was even beginning to think the PC didn't like me!
Regaurdless of my total inexperience, I kept poking around and fiddling with things, and my CPU thought it would imitate a Cuban cigar, but that's a different story. I bought a new MoBo, but this refused to work at all. After a month or two of fiddling, I somehow found out I had left out one vital thing in my installation. Spacers! 
I also specifically remember when first building the PC, looking at these strange little screws with threaded nuts on them. I thought they were so strange and neat!
I screwed them all together and made a little spacer totem pole and reveled in their mystery! 
All I can say in my defence, is you would think in two different MoBo manuals, you would get some kind of disclaimer about using spacers.
