question about his poster

What I believe happened is that the poster helped a lot to increase the fame of the Moulin Rouge, therefore making it more profitable. That's why the owner was able to sell it for "big" money and under new management the Moulin's act whas made tamer in order to make it accesible to better paying customers.

So the lewd act an it's dancers no longer had a place in Moulin Rouge, and were fired.

Dear Bo:

Here is some helpful info from the "quotes" page for "Moulin Rouge":

Henri: Big crowd tonight.
Zidler: Too big, thanks to your poster. Oh, I know I'm making millions, but I liked the Moulin Rouge as she was, lighthearted and hot-blooded, a little strumpet who thought only of tonight. Now she is grown up and knowns better. She has money in her stocking, wears corsets, and never drinks a drop too much. Worst of all, she never sees her old friends anymore. She has gone into society. Last night she entertained a cabinet minister and his wife and daughter. It's disgusting.

Hope this is helpful!