It's also because we deliberately chose to use "Day-mun" for things spelled daemon to differentiate from 'demon' which had other meanings that would ambiguate. Really, you have to know what fun it is to talk about demons in a public place and have to deal with the shocked and horrified expressions from casual onlookers. (in the late 70s. Now, of course, they'd just think you were a Buffy geek.)
I really like the fact that the full history of versions of Wikipedia articles is available. For example, the history of the Prophets of Islam page tells me that you had the bad luck to view this page between 4:28 and 4:36 on February 13. This seems to be quite an accurate page except during those six minutes. Occasional vandalism like this, followed by speedy reversion, is the price Wikipedia pays for speedy updates and millions of people doing useful updates: I find that it's worth it, on balance.
I was just in a networking class where everyone had the same text. The subject of daemon came up and the student reading the passage (including the pronunciation hint) pronounced it wrong. The pronunciation key was written in bold lettering, and he pronounced it out syllable by syllable incorrectly. What the...? My head about exploded!
Just another case of people wanting something to sound more fancy than it really is.
They are probably working off the general guideline from elementary school of 'when two vowels go walking, the first one does the talking' (which I was guilty of until just now after looking up the dictionary pronunciation).
Unfortunately there are just as many exceptions to the guides as there are followers.. so you end up with a mix of results. Potato, anyone?