1- Actually, I don't know that we really debated it much; this is the first time it's come up. We can debate it now. :-).
I'm inclined to agree that in the context of a 50-pixel widget with little room to explain things, "total" is probably the expectation.
I don't know whether anyone would have a cow if we switched from "active contributors" to "total contributors" in the widget. We have a lot of widgets in the wild now.
2- The person-years effort estimation is strictly an artifact of COCOMO, which I don't really defend. In my opinion, COCOMO often doesn't correlate with the typical ad-hoc development process of many open source projects (as opposed to corporate waterfall methodologies, for which it was designed). We provide it here because it's a relatively standard way to express the scale of a project to non-technical users.
Ironically, given the source control history, Ohloh could provide a very accurate estimate of actual development effort, but COCOMO is a "standard" and it doesn't use this extra information. Also, COCOMO is intended to include a lot more than just development effort -- it's supposed to estimate planning, discussion, testing, management, etc.
We can look into providing Ohloh's calculation of the total person-years from the source control logs as a new statistic.