The Duke's branch in Bangkok at the Emporium closed several months, but the good news is I hear they are reopening at a new location, Sukhumvit 33 at the former Coyote restaurant. In my opinion Duke's had the best "American" style food in Thailand. The old place was in a hard to find hidden location. I hope the new location does better. It's scheduled to open in August. The original Duke's is in Chiang Mai.
Another excellent "American" restaurant/bar in Bangkok, Woodstock, closed a few months ago. It was a Bangkok institution when located near Soi Nana. They lost their lease and moved a few years ago to Thong Lor 13. It was really an out of the way location in a Japanese neighborhood and never recaptured their customer base. Woodstock will be sadly missed.
Location, location, location.