Power buttons are somewhat special just from a hardware point of view; I don't think they are especially useful for this question.
You can't navigate a menu to reach a power-on function. A competing power button service will never come out to replace the currently popular power button service. Every single Xbox or PS3 owner will use the power button(s) with regularity.
He's referring to the center button on PS3 and XBOX controllers that goes to the xbox dashboard or PS3 dashboard, or the home button on the Wiimote, etc... at least, that's what I assumed. That button does count.
You can't navigate a menu to reach a power-on function. A competing power button service will never come out to replace the currently popular power button service. Every single Xbox or PS3 owner will use the power button(s) with regularity.