Probability of flopping set and being beat by flopped overset?

[RedSoxFan]

Ok- probably not a new question so I'll pollute the forum more.

What's the probability of only 2 players (6m and FR- assuming tables full) being dealt pocket pairs?

Given that probability, what is the probability that both flop a set? My intuition is that it's rather small.

So if my intuition is correct, why do I read so many posts about people worrying about being beat by an over set (both flopped)? I just read an idea that playing pocket pairs 55 and down is -EV because your set can beat by an over set too often. This is BS IMO. If I have 44 and flop is A94, I'm focused on stacking the Ax person and not worried about the chance that someone has 99. Is this wrong? Don't you think we're paid off way more than enough with hitting a low set compared to the infrequent times we're busted by a flopped over set?

I've played 20K hands (2 months Pokerstars) and have busted a guy with an over set once (but were both all in pre-flop AA vs QQ) and had my middle set beat once by an over set.