Well, they're different chipsets for different processors. The GIGABYTE board is based on the H55 chipset, mainly designed for HTPCs and lower-end budget computers for integrated video input. These boards are socket 1156 based and support Core i3s, Core i5s and Core i7 800s.
The ASUS P6T SE is higher end, enthusiast class socket 1366 motherboard with the X58 chipset for Core i7 900 CPUs, with dual 16x PCI-e lanes and triple channel memory support.
Are you really sure they're priced the same?