Showrunners David Benioff and D.B. Weiss acknowledged the likeness during the commentary feature on the show’s DVD box set, noting the decision to use the model was motivated by budget and not by politics. ”George Bush’s head appears in a couple of beheading scenes. It’s not a choice, it’s not a political statement. We just had to use whatever head we had around,” they said in the commentary.
HBO and Benioff and Weiss issued a pair of statements late Wednesday apologizing for the incident.
"We use a lot of prosthetic body parts on the show: heads, arms, etc. We can’t afford to have these all made from scratch, especially in scenes where we need a lot of them, so we rent them in bulk. After the scene was already shot, someone pointed out that one of the heads looked like George W. Bush," Benioff and Weiss said. "In the DVD commentary, we mentioned this, though we should not have. We meant no disrespect to the former president and apologize if anything we said or did suggested otherwise." (via)