The comma in "top of the message, or include just" shows that
two suggestions are being made, one suggestion is
bottom-posting and the other suggestion is not.

As you say, "It's just a guide" - not rules, but just a guide.

I see that you conveniently forgot to quote the author's
comments that the quoted bit below was just his own
personal preference and not a rule.

"mike" wrote in message
news
On Mon, 17 Jan 2005 14:23:02 +0000, Airy R.Bean wrote:
Conventions are not rules - if they were to be so, then everyone,
including you, would follow the convention of top-posting.
RFC 1855 - Netiquette Guidelines

- If you are sending a reply to a message or a posting be sure you
summarize the original at the top of the message, or include just
enough text of the original to give a context. This will make
sure readers understand when they start to read your response.
Since NetNews, especially, is proliferated by distributing the
postings from one host to another, it is possible to see a
response to a message before seeing the original. Giving context
helps everyone. But do not include the entire original!
It's just a guide - the rest of it is worth reading too....