Sure, both are entertainment in that they provide enjoyment to their fans. However, the one deals with deep issues of existence, identity, reality, and meaning, while the other deals with superficial issues such as which vampire hunk is going to hook up with which vampire babe (or so I presume -- I actually haven't read/watched Twilight or any other supernatural romances).
To the extent that art deals with deep issues of critical importance to humanity, it at least strives to rise above the mass of "pure entertainment" which does not strive for anything more than entertaining and distracting its audience from just such serious contemplation. To the extent said art succeeds in what it tries to accomplish, and does so in a profound, engaging, and unforgettable way, it is great.