I don't think it is intentional, it is how different people interact with the list and their proficiency with lists of this nature.
For example I use the web interface '
groups.google.com' and everything is organised into threads and clearly separated.
Others I assume subscribe to this as a mailing list and may receive it either as individual emails, or daily/weekly digests. It may simply be a matter of convenience for them to 'reply' to an E-mail thread/digest mail and continue the conversation (albeit potentially tangentially and non-thread related) that way.
Does that make sense? Happens all the time... on all mailing lists....