Bullet points from my Ustream talk in connection with Art Micro-Patronage's "10,000 Pixels" exhibit.
1. Pixel art is a web genre separate from gaming. You can find discussion boards dedicated solely to the publication and critique of pixel art.
2. Artists working in the gallery/art school tradition are attracted to pixel art because of the low level control it gives you over art-making. Some don't feel they are completely in control until they get down into the code telling this part of the screen to flash green and this part blue.
3. Every image on a modern browser is now "smoothed" as if it were a photo enhanced to hide grain. Pixel art flouts this trend and celebrates the artificial.
An area not specifically covered is the political or ecological argument. Products such as Siri suck enormous bandwidth and motivate needless "buildout" (more batteries, more cell towers...). The choice to work small is the web's equivalent of locavore dining.