Plenty of people have stumbled and rocked Hendo. Fedor blasted him with punches and almost KO'd him in their fight. Shogun had him on rubber legs in the fourth. Anderson dropped him with strikes, Wanderlei Silva in their first fight in pride, he was knocking Hendo over for fun with strikes. He's got great recovery, but he certainly isn't unflinchable.
None of Machidas strikes seemed to have any impact on Hendo what so ever. That's because most of his shots were grazing ones because he wasn't properly in range and because he wasn't fully committing to the majority of his strikes.