With a lot of CGI sets, V could do very well with its current ratings on cable. At least it (and every other show) wouldn't be forced into desperate actions like this:

V's March 15 season finale will kill off up to one-third of its cast! With only central characters Anna (Morena Baccarin) and Erica (Elizabeth Mitchell) safe, executive producer Scott Rosenbaum says two or "possibly even three" of the following actors have been let go: Scott Wolf (Chad), Logan Huffman (Tyler), Morris Chestnut (Ryan), Joel Gretsch (Father Jack), Laura Vandervoort (Lisa) and Jane Badler (Diana).

5.3 million viewers would be pretty big for any cable network. It might cost too much for that few viewers, but the broadcast networks aren't interested in trading down. They can cut costs on V, scale back, and make themselves more attractive. But ABC doesn't want that, because it doesn't want to have a series that only gets 5 million viewers at all.