In article <0001HW.BFF322F0000A1146F0284...@news.individual.net>,
Steve

Back in days of yore the only net users were technical, they produced
standards and guidelines and those are the interleave recommendations you
see. The RISC OS oriented newsgroups have always been a bastion of
technically oriented people and a few others who just liked the platform.
Since most of the techies used the approved layout the done thing round
here is the standards approved thing.

The technical reason applies more to the rather awful client that Microsoft
managed to produce which makes selecting text to be replied to more
difficult than it should be:
Outlook succeeds in driving me mad every time I select text from the
original by highlighting it and then click reply and the bloody thing
quotes everything rather than just my selected section.

Until relatively recently it was pretty well impossible to quote text even
remotely properly using OE or Outlook. ("Properly" being the > marked
fashion I have here - other characters are permissible)

Any time you have the odd day to waste people can list the faults in OE,
but I suspect you already know them.

Most of the others are probably commonly populated with users who came into
net use with top posting common in the first groups they used. (Many of
these net users probably think "kewl" is a real word.)
Old habits and all that. The converse applies, those who commonly use
groups where the longer standing members read the guidelines were told
early on what the correct version was.