Reasons vs excuses

Seth Godin’s post today on reasons and excuses for companies reminded me about something I’ve been thinking about for a while.
The terms reason and excuse are frequently used interchangeably, and the term “excuse” often has negative connotations to boot: “that’s just an excuse.” I think that’s wrong. An excuse should excuse you – it may also be a reason (and likely is), but the perception of it as a negative thing ought to be incorrect. A reason is just an explanation for why something happened.
This may be prescriptive grammar-GodwinsLaw-ing, but I think there’s some merit to the approach. There ought to be a distinction between a reason and an excuse, and I don’t believe that the English language as currently used really allows for that – which is ridiculous, given how many words we have.
(Today’s probably useless entry brought to you by a long put-off dist-upgrade on a group server from Ubuntu 5.10 to 6.06. Boring.)