Open Document files in Abiword and OpenOffice

[Graham Todd]

Often, when I write some thing in Abiword and save it in .odt (Open
Document) format, it is not recognised in exactly the same way by Open
Office. This is the same for text and formatting.

I thought the Open Document Format was a genuine standard, so in my
ignorance I assumed that all documents created by a word processor
supporting this format would recognise it identically.

Can anyone explain why this should not be the case?

Its often less memory intensive to use Abiword than OpenOffice (or
seems so) and that is the main reason I'm raising this query, but am I
correct in my assumption that all .odt files should be treated the same
way by all word processors claiming to support the Open Document
Format?

If not, how can I be sure that any person to whom I send the .odt files
will read them as I do, or be able to read them at all?

-- 
Graham Todd