And if WebTV doesn't do anything for you, think of browsers for the blind. Or browsers on Palm Pilots. Use of logical styles for character formatting is Good . Generally, an HTML author shouldn't have to worry about the physical formatting. But it's important to remember to not get too carried away by this, as you cannot have logical styles to cover all situations.
Redundancy is Good .
I think browsers should simply not display anything if the alt text is set to nothing and the person browsing has either turned images off or is not able to view them. Good spelling and grammar is Good . I don't think people should be anal about this, but it certainly helps in getting the information content across. Thinking about your markup in abstract terms is Good . You shouldn't have in your head when you write HTML what it will look like given the settings of any browser.