Imagine you have images turned off. You visit one of the sites. Obviously it's unusable because images are controls, but that's okay. But you notice that they're using a font colour that is very close to the background colour (eg light-medium blue on medium-blue) and then wanting to load an image in the background (white) that would provide the contrast.
You can't tell anyone because minimum karma requirements prevent making a meta-post.
Bug reports from naive users are probably horrible, but still, how many hoops do you want bug-reporters to jump through?
See this example for a hostile response to a reasonable question where it's assumed that people visiting the site need the buttons -- they don't. Most people will be reading questions and answers and will not have accounts.
http://meta.christianity.stackexchange.com/questions/4120/is...