No its not, most people (and some surgeons do not require it even with a band) are required to do a pre-op diet. Which one is recommended will depend on the provider. Not everyone is recommended the milk diet for each of the surgery types - a lot are given alternatives which follow low fat/low carb/low sugar and low calorie varieties, not everyone regardless of surgery follow the milk diet, but various alternatives.
Mine recommended a low fat, low carb, low calorie diet, but I personally chose to do the milk diet for 2 weeks. The length of time that you need to do it for, again will vary.
As with all of the pre-op diets its to prepare your liver for surgery, and this applies to bands as you're having laparoscopic surgery, if the liver is too big it could mean that you can't have surgery or they have to open you up.
length of time will depend on whether you're having SILS as well as your own situation and BMI. But more often than not, with a band surgery you can still expect to be doing a pre-op diet of some sort.