I'm not sure how many people coming to Scribus will know what a printing press is. Most printing these days is done with a home/office printer and, as Nermander says, a lot of "print shops" are just places that have a big laser printer. Also, as a.l.e mentioned, "press" for some people will mean "newspaper", i.e. "the conference room was full of press men".
I realise that a lot of printing is still done around the world on actual presses - especially where electricity isn't readily available - but if we're talking about doing something with the output from Scribus then it will have to go through some kind of digital equipment. And for most people it will be inkjet/laser printed.
I'm guessing that very few Scribus users will have their output put through a real professional print machine (whatever I mean by that given the number of different types) but I assume the ones that do will know more about what they're doing than the average user.
As has been said above, it's all a matter of wording and nothing will be perfect because of the sheer number of variations in processes but if whatever is used makes sense to the majority of users while giving the pros a way of doing things their way then that will help.
I added the "(CMYK Separation)" bit to the text to make it look scary to beginners - they'll stay away from it - but also to let the pros know what they can use if they want to but if that's wrong then I'm happy for other wording.
None of my stuff gets printed on anything other than a common or garden home/office printer so this is not my area of expertise but I'm trying to come from the angle of the "average Scribus user" (whoever they might be).
Just to add a bit more spice to the recipe: Maybe there's a better way of doing this. Perhaps there's a way of putting Scribus in "Professional Mode" that opens up all of the pro stuff (like CMYK separation, etc.) while "Normal Mode" only lets the user do stuff with RGB. The average user isn't troubled by options they don't know what they're doing with while the pros have all of the toys to play with. It's a thought, but I can't see it happening.
P.S. I like the idea of asking what the various options actually do though I'm not sure the explanation would fit into a drop-down box or a tool tip!