I'm no highly successful novelist, but I would disagree.
I've seen much improvement in the storytelling and technical skills in my novels due to my short stories skills continuing to improve. I've also read far too many published novels that are popular but rightly get slammed by critics for poor technical writing, or epic fantasies that ramble for sometimes a hundred pages or more without moving the plot forward or use page after page of narrative in their storytelling. There are things you simply can't get away with in short stories and I believe that learning to write short stories well can only improve your ability to write a good novel.
Also, though most of us won't end up doing as well as folks like Ken Liu, there are highly successful short story writers out there who haven't published novels (as far as I know), but when the do write one, I'm sure it will be good and they won't have any trouble finding a publisher!