If Republicans are so worried about voter fraud, why do they not mention this? (See details)

As we all know, various places have changed their voting laws to prevent voter fraud, and many Republicans endorse this move and deny any possibility of abuse. They also fail to mention that the Romney family owns the voting machines that will be used in some states.

So I want to know how it is that they can question the legitimacy of Obama’s birth certificate, yet not question the legitimacy of the 2012 election. Are they truly enemies of free and fair elections, are they just blinded by idealism, or is it something else?