A 'Small' font tag would be nice- I don't want to start a slingshot of other meaningless html tag requests, but a small tag could be useful.

Well, when a person posts something and they use say, bold, or underline. They are using typography; To bring forth certain elements in their speech/posts.

Example, say I wanted to write an article, or tutorial and I have comments that I'd like to add but don't want them to be too distracting. Thus making the font smaller would add a seperation from the tutorial text as opposed to using (){}[] with the regular font size to encapsulate the comment. Often I've found this distracts people from what they're reading.

you've got steps above the regular font size, all the Heading tags, but not a step down in size in relation to the normal font; So questioning this is as moot as using a step up in font size as well.

Footnotes, my son. Footnotes.

I'll start allowing <sup> so you can make them, properly ;)