Vector graphics are easier for storage purposes, but they are terrible in a couple of other crucial aspects that makes them problematic as an end-all-be-all graphics solution.
First, it is very very difficult to create a high level of detail with vector graphics without using several layers. If you want grunge, you do that one, lighting, shading, several masks and gradients later and you have something acceptable.
With bitmaps, you just paint it, and it's always one layer. Which brings us to my next point:
Vectors are much, much harder on the machine. Calculating them and redrawing them - especially when there are multiple layers involved(such as with one shape with a little shading) is time-consuming and severely limits how much detail you can allow.
The best solution to this is to simply draw in vector, and then render it to raster for performance purposes.
This is fine in theory, especially for simple shapes that do not require a lot of animation. But when it comes to animated vectors? Can't do it. You're back to loading it all onto the CPU or pre-rendering every animation sequence at the desired FPS.
My favorite middle ground is Anime Studio. Good cheap vector animations that can be rendered out to raster, but usually need a little clean up.
I'm going to have to look at SVG though - I've got something that has some odd collision detection requirements I'm hoping it can help with.