I'll offer another point of view, how about the Law of Commonsense? If a player goes over the goal-line with the ball tucked into his stomach and falls on it most sensible refs would award a try.
I'll offer a few scenarios.
1. Some of us may recall the Second Test in Dunedin in 1986. The Wallabies had won the First Test and were looking at only the second series win in NZ. Oz were a few points behind (2 or 3?) when Steve Tuynman went over the goal-line with the ball clutched to his stomach and time almost up. An AB went over with him and got his hand around Steve's midriff. The preening, prancing, ponce of a ref, Derek Bevan, ruled no try as he adjudged the Kiwi had his hand under the ball. Most (all?) players' palms aren't big enough to completely cover a rugby ball, if ANY part of that ball touched the ground it was a try. It's difficult to rationally deduce no part of the ball touched the ground, but Bevan did. I always got the impression Bevan took up reffing to give himself opportunities to show off his calves, such was his predilection for blowing the pea out of his whistle while standing on tiptoes.
2. Many years ago I witnessed something similar while watching a grade game in Brisbane. This was, of course, in the pre-TMO days. A mess of players went over the goal-line with the ball-carrier at the bottom. The referee instructed all players to keep quite still, then he peeled them off one-by-one until only the ball-carrier was left. As he was over the line with the ball clutched in his lower stomach the ref awarded a try. In this instance the defending team didn't object, in fact they were quite complimentary towards the ref at post-match beers.
3. Me: while running the line for the Pirates in a second grade match at Chatswood many years ago the ref awarded a try without sighting a grounding. Play was at about the half-way line with the Pirates attacking when there was an intercept (match officials hate intercepts. There we are wandering up the field in one direction when some colt, much faster than us, grabs the ball and dashes off in the opposite direction). The Pirates full-back tackled the Gay Gordon as he went over the line. I couldn't see a grounding as I was too far away, and signalled this to the ref after he looked at me to see if I did. After I put my hand across my eyes to show I was unsighted he signalled try. Post-match he confirmed to me he used the Law of Commonsense, he said it was difficult to imagine how the Gordon player couldn't've scored in the circumstances. I agreed.
4. The Brumbies no-try. At no point did the TMO advise Gardner the Brumbies player dropped the ball, although replays did show it moving down his front; if the ball was in contact with both his stomach and hand we must presume it wasn't dropped. There are now replays to look at everything recorded, what about the ref instructing all players to keep completely still, as the old bloke did in Brisbane years ago, with the threat "the cameras are watching you, move and all bets are off"? Then he could've peeled off the players one-by-one to see if the ball was over the goal-line, time-wise it wouldn't've taken any longer than most of the contentious replays we get these days. I reckon it was and a try should've been awarded. A bit of imagination and a lot of courage could've helped here.