Don't blame Webster. For a lot of the well-known differences, he actually preserved the original.

In particular, the British added the "u" when French was in fashion, and likewise for "-ise" (in fact, "-ize" dates all the way back to Ancient Greek!)

One thing that Americans do get wrong is misspelling "-lyse" which comes from a different Greek root, so should not follow the same pattern as "-ize". But even then, Webster didn't invent the error.