Because he didn't specifically say he was going to buy ONE 16 GB. RAM kit and many people make the false assumption that they can just buy (2) 8 GB. RAM kits of the same part number and run them at the advertised latencies and frequencies of ONE RAM kit, which Corsair specifically states may NOT be the case.
In addition it's easier on the IMC to use (2) DIMMs over (4) DIMMs. Some mobos also limit OC'ing when (4) DIMMs are used forcing the RAM to be run at the default frequency for the CPU.
The bottom line once once again is that mixing of RAM even of the same part number can have issues, i.e. could require slower latencies or higher voltage than a ONE, matched RAM kit of 16 GB.
Edited by AMD4ME - 5/29/12 at 6:54am