The network advantage is hard to disprove. But which has lower total computation cost?
A bitmap is created once, and the idea is very basic - you have a grid of pixels. The good part is that it's simple to use it. A vector image is a recipe for making an image. More calculations have to be done client-side, times the number of clients. Clients have to do the work the server didn't want to. You could say a bitmap is a compiled vector.
I think an ideal solution might be treating vectors as a source code. A web server would receive a request, including display size. Then it would "compile" the vector image into a bitmap and send the bitmap of the right size. And cache the image, so if another user with the same display size asks for the image, it's ready. Few people resize the browser window often. For the same reason, I think code highlighters shouldn't use Javascript on client side, unless the code might change (like, an in-browser REPL or pastebin).
Am I being misinformed? Pedantic? I like vector images, but would like to learn if my affection is justified.