I imagine it has to do with the size of the original file that the person used to create the Youtube videos. Youtube has a maximum file size of 100 MB, and I've seen MPEG's of the Stooges shorts that are 200 - 300 MB or more in size. I imagine that the person who uploaded this to Youtube had a large file that he edited into 3 smaller pieces to get under the size limit.
The guys who made the "Here Comes Flossie" video available, on the other hand, have been doing this sort of thing for quite a few years, and apparently are better at making their initial filesize small enough to start with that they don't need to break it into smaller pieces. (I've seen 2 hour movies posted on Youtube in a single file, so it is possible to do that.)
