OCing the ram or even getting it to run at the manufacturers stated speed and timing with all ram slots populated is more difficult, but it's not a deal breaker, just takes a little work. Contact them and ask them why.
OMG, I just checked out that site and looked at one of their 980X OCed systems and they are raping you. I took the parts and replicated it at Newegg and the cost here in the US would be $3,500 + the water cooling, another $300 or so, for a total of approx. $4000.00 and with the exchange rate and additional cost because of the vat, there are charging approx $2,000.00 US to build and OC the computer I looked at. That is some serious profit.