Kid's like it because it's funny. Once the story ends it starts all over again at the bucket and the hole. Kid's like paradox's, I know I did. In my mind its a song of vindication for Henry. At the end we realize that Henry's first question was not so dumb after all. We've come full circle in our understanding of the situation, one that Henry had all the time.
How often have you been beset by the same issue? You know the full scope of the issue and the first/common sense approach simply doesn't work, yet the only way to make someone else understand that is to allow them to figure it out for themselves or even guide them along the way with a few "helpful" questions. Being a software developer and an acro/yoga teacher I feel like I'm often in that situation. The best way to understand a problem is for most people to figure it out themselves. Simply telling them the answer doesn't always work. So just like Henry I take the time to walk them through the process. The process I've typically already solved. Allowing them to discover the answer themselves ... with a little guidance.
An answer someone comes to through their own process or through a guided process where they work through the steps always seems to lead to better learning. When I was younger I found having to lead someone along to be so pedantic. Why can't you just see the answer? Everyone learns differently and if you want someone to learn or understand something then you have to accommodate them and the way they learn. Give them the tools and the situations that allow them to figure things out for themselves. Not only will they learn faster but they will remember better. Just like Henry lead Liza to understand the paradox of the hole in the bucket! I bet she won't be so uppity the next time Henry asks!