While on the topic of polo coats in pictures, I recently pulled out my "Pimm's Book of Polo" (something I bought on a lark when the second incarnation of Abercrombie & Fitch was clearing out its real stock to start selling tee shirts and thongs).
The book has a couple pictures of very stylish Indian players wearing polo coats while accepting their trophies. The pictures appear to be from the 1920s or 30s. Their coats are fully belted "wrap" style, without buttons. This makes perfect sense since they were to be thrown on between chuckers.
Since I have read that the British adopted this style from India, my guess is that the British tailors took the camel coat wrap, and added the double breasted aspects typically found on Naval great coats, or British Warms or Ulsters.
And, of course, us Americans have Brooks Brothers to thank for bringing it to here.
I just think the evolution of the coat is interesting.