About a kid with a widowed parent who is magically transported into a book world - Last Action Hero is basically the same thing, except geared to appeal to 90's kids - it's not as good, it's less serious, but it's very enjoyable none-the-less.
The point of this movie is that its a spoof of all the cheesy action films out there. They did this by having a fake action world that they made as ridiculous as possible, and a real world with our set of physics to contrast it. I think everything else comes from that.
Danny's mom is widowed because it was an easy way to write a father out of the story and have her be too busy to keep an eye on Danny. That gave him time to hang around the theater all the time and skip class. It also made his character lack a father figure in his life and explained why he was so fascinated and attached to Slater.
I actually havent seen Neverending Story, so maybe there are more similarities between the movies than I realize.
I noticed the similarities in the exposition right away, so I had it assumed that the spoof of action movies came later in the developmental stages. I could be totally wrong.
I did think of another correlation, and that is in both films the main villain is from the fantasy world and is aware of the existence of the real world.
Although, something just occurred to me. The main character of The Neverending Story himself didn't exactly travel into the book world. You need to watch it, I don't want to spoil it. It's a great movie.