See, I'm the opposite, I feel that the Moria stair sequence, while it had some great parts, really lost me with the tilting stairs in a way that The Hobbit didn't. I just couldn't bend my suspension of disbelief enough that I could feel that Aragorn and Frodo could tip the stair.
They didn't tip the stair on their own... the stair would probably have tipped as it did anyway, but their presence might have tipped it in a slightly different direction if they had applied their own weight in a different direction... so Aragorn wanted he and Frodo to reinforce the stairs' natural tilt by leaning forward.
Anyone can be cynical and say that this was still impossible, just as they could say that the bridge/ladder/pole stuff in the Hobbit was impossible. I actually thought that bit was entertaining, to be sure. But I wasn't involved in it. It didn't feel as big or as important as the tilting stair sequence. And it didn't serve to accentuate or develop the characters anything like I've demonstrated about the Moria sequence.
The other point I wanted to make in my post about the points I liked about the Moria sequence was how, when Frodo and Aragorn made it across, Howard Shore kicks in with his most bold use of the Fellowship theme... it truly symbolizes how together they were at that moment, after Aragorn and Frodo (normally the most isolated guys in the group) had made it to their friends.