Do you realize that the 16gb of memory alone would cost you about $1000.
The 4gb Dimms which whould be required have just been released and are priced crazy expensive.
You would be better off with a Workstation Device at this point which have more Dimm slots.
But a more direct answer, is that the only Chipset that supports Intel Chips and 16gb of memory at this point are the P45 boards which don't have on-board graphics.
Some AMD solutions have both.
However, none of the Motherboards has more than 4 Dimm slots so the price of memory will be crazy.
Technically some boards have more than 4 slots, but in such cases they are simply to allow for the use of DDR2 or DDR3. You cannot populate all of the slots at any point in time.