"Reality" is something new to the WWE only. After years and years of a purely fantasy "universe" with rather non-believable characters involved in some pretty far-fetched storylines suddenly "out of nowhere" CM Punk "breaks kayfabe" and "shoots" all over the place, and WWE fans believe this is something new, never seen before, and they are calling it "reality". More specifically, the "Reality Era".
Truth is, since it was introduced into pro wrestling by Paul Heyman's ECW in the early 90's "reality" has never gone away. We just don't see it in the WWE. Most fans watch only the WWE so they don't know any better. We, ALL of us, have to understand that there is pro wrestling and there is the WWE. They are not the same thing. The most realistic pro wrestling promotion in North America is ROH; they don't try to BS the fans or think the fans are stupid. They try to keep things as realistic as possible and (almost) everything you see in ROH is believable. You don't see ROH fans complaining about anything that happens in ROH or damning the "writers", because it IS realistic and believable.
But the thing with the WWE, and it doesn't seem that anybody is SEEING it, is only the Punk/Cena/Triple H angle is based on "realism" and that's only because Punk "broke kayfabe" and is doing those "shoot" promos. The rest of the WWE has not changed. That angle is getting over because Punk is saying things "that aren't supposed to be said" and we're enjoying the scandal. Reality is, other promotions have been doing this all along, TNA especially.
"Reality" is good, it makes things seem more believable. But if you only have one "reality"-based storyline in the show it makes the rest of them look more non-believable and made-up.
To respond to your Punk/Big Show example: recently, Brian Kendrick (all 180 pounds of him) beat the 350-pound Abyss for the TNA X Division Championship. Looking at it on paper you'd say "how is that possible? Abyss is a foot taller and nearly double Kendrick's weight!" Well, Kendrick had a game plan, stuck to it, and wrestled a smart match. He stayed out of Abyss's grasp, used his speed, stuck and moved, hit and ran, and waited for Abyss to make a mistake. When that happened Kendrick capitalized and beat the enormous monster. Yeah, it was an upset, no question. But it was believable because Abyss underestimated Kendrick's skills and desire to win and Kendrick did wrestle smart.