Minor differences in manufacturing will affect these things. Model F, like the Model M, was produced over a fair period of time. Brand new ones will sound different from older ones because the older ones are more broken in, and dust and dirt can still affect any switch even if you otherwise can't see or feel it. And because it's a relatively old keyboard, we can assume that fabrication for old models just wasn't as refined as it is today, so there will be differences in how they feel or sound even when compared to a completely accurate reproduction.
It still happens today on more common and "refined" switches (refined being a relative term here). As far as I'm concerned, it gives each keyboard its own character, so I don't see it as a bad thing. It only becomes a problem to me when one switch on the same board has a wildly different feel from the others.
As for why they sound different on Youtube than yours does, that's easily explained by a mix of your speakers and their mics. I don't think even the best microphones and speakers on the market today can 100% faithfully reproduce any real world sound, and most Youtube reviewers don't have access to the extremely expensive/highest quality stuff anyway.
