For images that are purely decorative including an empty alt attrib is valid. People using screen readers (and people with images turned off[1]) don't need to hear (or read)"SMALL RED BULLET" for all 7 items in the list.
[1] I often have images turned off. I'm using a mobile broadband dongle. My ISP uses horrible proxies to compress images. I'm in the UK. The IP of the proxies is 1.2.3.9 through 1.2.3.12 - this is sub-optimal for many obvious reasons. Bypassing this proxy is trivial, but means I download a lot more data.
I typically use "-" or "*" as an alt for bullet images in text, and similar decorative markers. It seems to make more sense to me to emphasize that there's a list.
The only reason I'm still using them is that they don't charge for MB or GB; I pay for three months and get "unlimited surfing". They block some stuff after you hit 1GB, but that's trivially easy to get around. Which I do, since they've said I get unlimited web use.
You can't solve a social problem (content providers who don't care) with a technical limitation (required alt tags).