DFI has more than just 10 RAM options dude.
It's the quality of the materials used to make the board, the BIOS options, the BIOSs made for the board things like that. When I say the quality of the materials, I mean things like japanese capacitors which is what DFI uses....they provide the best quality for capacitors meaning the likelihood of them failing or being unstable compared to other boards that don't use them is slim.
Being able to retain good stable voltages, a highly optimized BIOS and things like that make it the best OC'ing board.
People know the max of their CPU because they test it....you can only push a CPU so far before it simply won't be stable....same thing if you're lifting weights...50lbs might be easy, 60lbs might, and you'd just keep going until the bar falls and crushes your neck, then you know next time to not go as far.
The point is, the DFI DOES overclock better, rather it doesn't 'overclock' per se, but it is the best choice for making sure you get all the potential out of your CPU and RAM that you can....it's not world reknowned just for the hell of it ya know.
DFI is mainly for the enthusiasts...it's "Complicated' because mainly it has all those RAM options to tweak and get every ounce of performance out of your system...it's this attention to detail to try and make a board for those who really want to get crazy with their hardware that also makes it the best out there.
Yes the chipsets are the same, nforce4 is nforce4 is nforce4, but the chipset doesn't really directly effect your overclocking.
As for whether or not via does worse/better than an nforce4 chipset, well all the makers who use via chipsets aren't reknowned for having top quality boards made for OC"ing