I agree that the meaning of dcterms:source is different from the stated meaning of dwc:occurrenceDetails. The latter term originated with OBIS as 

recordURL - Gives the web address of the page where more information on this particular record (not on the whole dataset) can be found.

and was re-cast in Darwin Core 1.4 as 

relatedInformation - Free text references to information not delivered via the conceptual schema, including URLs to specimen details, publications, bibliographic references, etc.

and is currently defined as

occurrenceDetails - A reference (publication, URI) to the most detailed information available about the Occurrence.

So, one could argue that the dcterms:source is not necessarily the most detailed information available, and it would certainly not be only about Occurrences. 

So, occurrenceDetails certainly is no substitute for dcterms:source, and dcterms:source doesn't exactly circumscribe occurrenceDetails as defined. Nevertheless, the concepts are so nearly the same in definition, and certainly in intent, that I propose that adding dcterms:source obviates the need for occurrenceDetails as it will sufficiently cover the intended use of occurrenceDetails while allowing the same for all record types.

On Tue, Jul 5, 2011 at 1:12 AM, Gregor Hagedorn <g.m.hagedorn@gmail.com> wrote:
I think the two terms are different.

my understanding is that dcterms source expresses a relation between a
(usually digital) record and another record, that is derived from the
first.

I think this is very useful in DwC in cases, where records are taken
directly from a publication.

However, it does not replace the fact that the source of the record is
the digitization project of collection X and that the record is also
cited in a recent publication.

I have doubts whether occurrenceDetail is a good label for the latter
concept, however.

Gregor