No reason not to make a change. It's purely cosmetic. And the suggested one still works. Yes the "Difference" between Advanced and Casual is more than just word count. It's also component requirements. Both still require near-perfect Grammar and Spelling.While I see your point, I unfortunately doubt that a title change for the Casual/Advanced split will ever become a reality. The suggested one especially, since the Casual/Advanced split stands for more than just word count.
And a longer story would "need" more than a short story component wise. It's not that much of a leap and completely bypasses the Casual/Advanced prejudices.