"Seuss himself later revised the 1937 title Mulberry Street, saying that: “I had a gentleman with a pigtail. I colored him yellow and called him a Chinaman. That’s the way thing were 50 years ago. In later editions I refer to him as a Chinese man. I have taken the color out of the gentleman and removed the pigtail."
http://www.theguardian.com/books/202...ishman.”
The article makes clear that the sales of the books are increasing, in the US in any event, which feeds into the theory mentioned by several posters in this thread that that may have been a tactic.