Is "ego depletion" the only explanation for the experiment? How do the researchers rule out other explanations?

Maybe people choose the cake because they think, "Phew! I did something difficult! I deserve some cake!" And the people who only memorized two numbers think, "Well, I didn't do anything that warrants cake. I'll just take the salad."

I don't mean to propose this as an alternate explanation -- it just seems like there could be a million explanations for why people are more likely to choose the cake. (But maybe the researchers found ways to rule them out?)

Another random question -- have people replicated this experiment? Just curious.