It actually is because unlike you, many of us happen to live outside the US and are not allowed to shop on newegg and yes they do go out of their way to find out if you have a non united states credit card and they block you from purchasing anything from them.
They don't even care if you have a US credit card but you are traveling in Europe etc they will still block you.
Not sure whats the financial gain by Newegg doing this however Amazon is the richest online seller so kudos to them for accepting international credit cards.
Ok fair enough. Quick tip for Amazon to price match:
See on the product page if you scroll down below it says:
"Would you like to update product info, give feedback on images, or tell us about a lower price?"
Click, tell us about a lower price and enter the data from Newegg or anywhere else you found a better price online.
For example, you should enter
$99.26 for the PowerColor R9 270 card due to 7% off and $30 rebate on Newegg right now, shipping $0.