More Tolkien

I'm reading The Fellowship of the Ring, and I recognized something Tolkien did with the structure similar to what he did with The Hobbit.
If you read my recent post about The Hobbit, you'll know what I'm talking about: instead of one disaster in the middle of Act II, there were two.
Same thing with The Fellowship. After a very long Act I (but never boring; Tolkien is the master of Telling, which deserves its own post), Frodo, Sam, Merry and Pippin leave the Shire, and go into the Old Forest. They get LOST. Then, after their long adventure there, they get captured by Barrow-wights on the Downs. Tom Bombadil rescues them, and off they go to Bree, meet Aragorn, and that pushes them into Act III (I think).
Neither of these really forces them to change their plans, but the story still works. I don't know why. It just does. Probably because they really are disastrous, but (without looking very episodic) they keep the characters spinning and busy, until they reack Bree in safety.
Or not.
Just things I notice.