I suppose a compelling argument for them should be in order... well, I'll try.
One may ask why captions are necessary for something that can have a para follow it (to almost identical rendering effect).
Well, let me answer that with a rhetorical question:
Equations and figures already have captions; why are they allowed there? Well, one reason is that caption has a clear semantic meaning, especially since it is inside the element to which it refers. Another reason is that it simplifies xi:include for those elements.
All I want is to have the same capability for db.cals.table.
I have already submitted an (easily adaptable - it is actually for a customization layer - ) stylesheet patch for correct rendering of captions in cals tables.
P.S. I am quite perplexed as to why caption is used as the title of db.html.table.
DocBook mailing list thread:
please allow caption in CALS tables in DB 5
related sourceforge item:
db5 db.cals.table w/ db-xsl-1 generates double caption