I know this was posted a long time ago, but I just thought I'd add my thoughts.
For me "a la carte" in English, while I totally agree that it comes from the French for "by the menu", does not mean to me that you order from the menu instead of a buffet. Most restaurants don't have buffets, and you order from the menu all the time, but you wouldn't call it ordering "a la carte". For me anyway, "a la carte" means that you order something that isn't listed as part of a meal on the menu, that is to say, you order each item separately. For example, maybe you feel like chicken, salad and vegetables, but all of the chicken meals listed on the menu come with potatoes and a biscuit. So, you would order the individual items that you want "a la carte" instead.