that is because xeon is the server end processor and it offers
higher memory support 750 gb vs 32 gb of the i7,
higher memory band width 42.6 vs 25.6 for i7
4 memory channels vs 2 in the i7.
xeon offers 40 PCIE 3.0 express lanes and the i7 offers 16.
not to mention 15 mb l3 in xeon vs 8 in i7
for diff between QPI (Xeon) and DMI (i7): http://forums.guru3d.com/showthread.php?t=309126
So the xeon is overall a more powerful cpu in terms of the hardware that it can support and run though it's clocked considerably lower.