On my realm, pugs routinely cleared ICC on normal, and several did multiple heroic encounters. I regularly did GDKP pugs where we cleared 5-6 heroic bosses, plus Lich King. I ran a pug on an RP server that had no problem going 6/12 normal 10, with people in fairly awful gear.
As I said above, on my realm at the time, we routinely had pugs clearing the instance and doing multiple heroics. Mine was not the only server like this.LK normal was easy? The top 500 25m guild I was in who finished all hardmodes wouldn't really agree with your statement.