The informal buffet type of eating is on the top level, I think it is called Kings Court and then they have different resturants depending on which type of room that you are in which I do not agree with as we all have to mix together. It is not like a train or flight as we have to spend a long time on the ship and use all the other facilities together. The top rooms have a private area for sunbathing aswell. It is not a problem but you can feel excluded which is a bit much on a ship. But saying that the people who are in these rooms seem to be nice generally.
Yes there is informal buffet style on board both available at lunch and dinner. However one of the things that makes a Cunard cruise stand out is the opportunity to dress for dinner, particularly on formal nights.Other cruise lines such as NCL make a virtue of casual dining, so I suppose it is horses for courses. Yes there are parts of the ship reserved solely for grill level passengers but this is no different than there being first and second class area say in a railway train. It is only a problem if people let it become one by either people resenting it or by people taking a superior stance .... neither attitude is appropriate.