Public domain software is explicitly approved as "open source" by the OSI, and it is listed along with other licenses in their own literature, so I've put it back. --LDC
They seem to be awfully quite about PD software over at OSI. I was halfway through a response saying how I couldn't find any references to PD software on their webpage, when I came across the change history of the Open Source Definition: 1.2 – added public-domain to clause 10., and 1.4 – Now explicit about source code requirement for PD software. It isn't, however, listed on their "approved licenses" page, which threw me off. And so, your revision stands. I'll just add that the source code must be available. -- STG