What exactly is the main deference between entry level boards and high end gaming boards?
In my opinion, not much that matters.
Only if you are planning on multiple graphics cards will there be much of a difference, so long as the other features you want are there.
Like usb3.0, or 6gb sata. You probably only need multiple graphic cards for a 2560 x 1600 monitor, or triple monitor surround gaming.
Like Jack said previously, one of the big ones is voltage regulation. Some are just basic and some have elaborate multi-level power. Checkout the Rampage III for example (from ASUS web site):
Extreme Engine Digi+
[Extreme Engine Digi+] Powerful combination of analog and digital design elements
Extreme Engine Digi+ equipped with high performance digital VRM design can easily achieve the ultimate performance with adjustable CPU PWM frequency. It expedites heat dissipation and achieves better electric conduction keeping critical components reliable. Now you'll be able to push your spanking new Intel CPU to the limit, hitting benchmark scores that others only dream of. Extreme Engine Digi+ balances the need for voltage and the desire for rock solid performance to bring the ultimate user experience.