no tread overhang on last step onto deck?
 

is it usually ok, and code correct to not have an overhang on the last riser where you would step onto a landing or a deck? like in the attachment pic

If my nose were missing.....

I would have to say that this is fine as the deck surface won't short you on the required depth of the tread (11").

But seriously, what purpose does the bullnose serve? Is it a safety issue, or is it a drip edge, or what?

Well I don't think it's a big issue?

I know i started this with a joke, but i started wondering if something so common as a nose on a step is just continued out of aesthetics, or does it serve a purpose.

There are probably, buried deep in the files of some government agency, statistics on how many slip & trip accidents happen on steps with a nose as opposed to steps without one.

I can see the satellites linking up now, rows of computer banks being activated, whole buildings of government workers being called in for over time trying to answer this question. All I can say is, I've done it both ways and never had a problem either way. I'm sure there is some obscure OSHA law I've broken and will be held accountable somehow...