This is XC bug to me, I am sure QT will call it improvement
It has been like this since Clean URLs was first introduced. I am not sure why it was decided to just copy the words from the title and not make them all lowercase to begin with.
The js solution above will get you by only when you create product or modify it in admin. If you are importing products or do auto populate Clean URLs form maintenance page this will not work. The php script involved still outputs the words as they are - so capital letters.... You need to change the outcome in include/func/func.clean_url.php as well