I flipped through one of my Dell Tom and Jerry comics from the 50 a couple of nights ago. They talked in those. I really think that phenomenon in general wasn't some of poor research or laziness on the part of the writers, it was just putting what would make a good comic ahead of licensing concerns. Like Mark Evanier said in the article I linked, it didn't matter that much in those days because it wasn't like the kids saw the original source material that often anyway.
Sometimes these licensed kids' comics do some interesting things on their own, too. Like all the good characters created for the Disney comics like Uncle Scrooge. Or they can make use of characters that don't get much play in the cartoons. For instance, I heard Lola Bunny actually got some good stories in the modern Looney Tunes comics even though most people didn't have much use for her after Space Jam.