On my radio show I do only play 45s as it drives my collection and I like to discover unknown records and it results in a specific format / sound of my show. I pretty much don't repeat songs because I treat every show like it's a mix and listen to it repeatedly over the week so I don't want to hear the song all the time. I spend around 4 hours getting ready for each show (not counting all the time I spend looking for records).
I'm not inherently opposed to people playing CDs or downloaded mp3s (assuming they are high bitrate mp3s) on the radio, part of the problem is that you have to be really deep and obsessive, to the point of collecting mp3s of unknown stuff and trading them, in order to have an interesting show. Otherwise you're just playing well known stuff and the show isn't interesting (to me at least). The listener might as well listen to a CD.
However, 90% of radio listeners aren't interesting in hearing obscure "deep" cuts, they want to hear what they know. So playing CDs for that kind of show makes a lot of sense. I'm not inherently opposed to uninteresting shows, I just don't want to listen to them. I don't have a problem with other people listening to them.
This to me is also the most compelling argument for "OVO" in clubs. I'm sure most northern soul fans want to hear the songs they know and that's fine, they can go to clubs that play that music on original or non-original vinyl or CDs or whatever. But if the point of the "rare soul scene" is to hear new and interesting things, the act of collecting and finding records on your own and finding your own sound is what makes you a good DJ. Of course, there is also the problem of rich people just buying their way onto the scene by buying whatever Butch plays or whatever else is hot. I don't see the point of trying to get records that other people have just because they're popular, to me that's just as bad as not playing original vinyl. A good (or at least interesting) DJ should be experienced and should have gone through the experience of discovering different songs / tracks on their own and finding ways to make them into coherent sets.
I never thought i would make a pro-original vinyl only post, I guess what I wrote above to me is the most compelling reason for it. But like I said, I think paying a lot of money to get a currently in demand original just so you can play it in the club when it is "hot" is just as bad.