Like on domestic and short-haul flights, buy-on-board (BOB) menus often seem to be replacing complimentary meals on transatlantic and long-haul flights. US Airways has introduced DineFesh, a premium meal option which is to be purchased at least 24 hours prior to flight. Promoting premium meals may be leading to more robust BOB offerings in the future.
However, some of the airlines like United Airlines, Virgin Atlantic and American Airlines are not supporting the BOB concept for long-haul flights and have stated they are committed to offering complimentary meals.
More information was in an article on the apex.aero blog, which is no longer available.