Okay, I haven't read through the entire thread, so this is just my take on what Snowth said.
Snowthie, in theatre we have what are known as "Stock Characters". Characters that are basically the same and or used to bring the same effect on a play. They are not often used nowadays, but when they are used the plays may at first seem like copies of plays that have come before them because they use the same basic characters. The character styles work well together and provide a pleasant balance to the performance.
Now, think of this: the same idea can be and has been used in books, film, animation, etc.
The snobby, self-absorbed character; the brainiac; the cute one; the rational, advice-giving one; they all work well together to create a very smoothe plot-line. These characters were actually originally used in theatre during the French Renaissance.
As far as animation goes, these characters can be seen in many cartoons. The plot may be changed, but generally the "stock characters" are used, from Mickey Mouse to Scooby Doo to the Smurfs to Alvin. It isn't plagiarism. It's tradition, and it's what works.