All of the above and more. I'm thinking you are noticing them more for the same reason you notice camry's on the road after purchasing one.

I don't know that rails get replaced more often on Club Date drums, but if they do, I wonder if rail placement might have something to do with it. The rail on my 20" bass drum is at about a 10 o'clock position from the player's perspective. That wouldn't work on a clubbie since a tension rod would be in the way.

Yes, it could be anything, really. People used to alter their drums more in the "old" days because, for one thing, hardware options were more limited. You either worked with what you had or you came up with some kind of idea to make it more comfortable...or look "cooler". If I had a dime for every bass drum I've seen that someone attacked with a drill, then I'd....um....have a lot of dimes! Anyway, it's common.

I'd echo all of the above, that's a two hole mount right? Seems like it wouldn't be the sturdiest mount around. But yeh, there has been a lot of bass mount alterations over the years.