I think it's much more fundamental than that. Peoples attitudes have changed over the last 10 to 15 years and demands are much higher.
I've seen quite a few Everton sides over the last 40 odd years booed off the pitch, but it's only relatively recently that I've heard so many fans give players dog abuse for making a mistake
You're right though. When we start winning the boos will stop, but they'll come back very quickly when we play poorly.
It's not unique to Everton, and it's not unique to Martinez, it's become the norm except for newly promoted teams or teams where expectations are lower.