I agree with you actually. Watching the fight I remember thinking GSP would get the nod, but, I think the argument is Hendricks should have gotten a 10-8 in that fight, which would have made him the winner.
Really the only argument is that Hendricks won round 1. If you give him the nod in what is almost universally thought of as a tight round, then you give him the win because the other rounds were all clearly delineated.
Hendricks won round 2 and 4, GSP won 3 and 5. Your choice of winner depends on how you scored round 1 and because it was a close round, the issue is in doubt. I personally think Hendricks did enough to make the case for the round because when GSP would clinch up with him, Hendricks would land these vicious knees to his legs as a way to counteract the clinch and it seemed really effective. That said, I had absolutely no issue with GSP taking the round because of the takedown, the sub attempt, and some effective striking throughout. It was a close one, but on subsequent views I thought GSP 1, 3, 5 was a quite valid way to assess the fight.
There was no case for a 10-8 particularly by the old standard of judging a 10-8. Hendricks won round 2 but 2 is the round that gets most blown out of proportion of any round in that fight. I consistently hear things like Hendricks almost stopped him. It's such hyperbole. The fact is Hendricks clipped GSP with a good combination and visibly wobbled him. That's it. No knockdown. No subsequent ground and pound. No ref saying, "Georges, fight back." It was a moment of being visibly rocked and then quickly recovering and getting back into the fight.
The intriguing thing too is that GSP starts to take over the latter half of that round. Of course Hendricks' damage was by far the most effective offense of the round and he therefore obviously deserved the nod but some people will construe that one like it was Edgar vs. Gray II round 1 and it couldn't be further. GSP got stumbled and then recovered and did well for himself. Johny landed some vicious shots but did not come close to closing the deal in that round.
Hendricks' best round is actually round 4 where he gets GSP on his back and surprisingly manages to keep him there and ground and pound him for the remainder of the round. How many people can say they've taken GSP down? Even fewer have kept him there for a prolonged period of a round.