I think it's important to make the distinction between the Shockwave Flash format and Adobe Flash the design tool.
Adobe Flash the design tool is by far the simplest and most intuitive tool out there for designing web graphics, be it in vectors or pixel-perfect raster graphics. Not to mention its combination of layers and timelines which allows you to do a lot more in less time. The whole animations / ActionScript thing is just an added bonus if you're feeling frisky.
Most people use Photoshop for web graphics but that's wrong -- Photoshop was meant for photos. Others use Illustrator but it is way overkill unless you're doing fine arts or complex illustrations.