Usage of 등 to end a list where "etc" doesn't make sense
I know the meaning of 등 as "etc" or "and so forth", as in the following:
사자, 호랑이, 표범, 집고양이 등은 고양이과에 속한다.
But sometimes I see it at the end of a "complete" list, where "etc" makes no sense. For example:
무지개가 빨강, 주황, 노랑, 녹색, 파랑, 남색, 보라 등 일곱 가지 색으로 구성되다.
(The rainbow consists of those colors exactly, so "and so forth" shouldn't be needed.)
지용성 물질은 A, D, E, K 등이다.
(This is giving a specific list, again where "etc." would make no sense.)
The only explanation I can get is that, in this case, it means "the above inclusive items". Does that make sense? What is the purpose of 등 here? Is it necessary in the above examples?
감사합니다!