1 – A well written adventure can (often) be put into any setting, as supposed to a sourcebook that describes people, places and society in a more specific setting. Source books can also be adjusted, but it takes more work.
Actually, I generally see/believe that it is the well written ones that are setting specific. The generic ones tend to be, well, too generic to have flavor (and, thusly, not be good).
2 – It is much faster to prepare for a game by reading an adventure instead of a source book.
Depends upon the size and complexity of the adventure, but I would agree to this in a general sort of way.
3 – I think it is faster and thus cheaper to produce an adventure than a source book.
Like 2, above, maybe and then maybe not. But that isn't the main factor in producing adventures (or in the lack of producing them, actually). The fact that out of a game group, it is generally the GM that is the only one to buy an adventure - as opposed to setting material - means that less than 1 out of 4 (probably higher) gamers is buying adventures on a regular basis. When that pool is not huge to begin with....
4 – When I have read and digested a source book then I have an environment to play in but not necessarily a story to play. I already have lots of fun stuff for the environment, but like input on cool adventures to play out in them.
Yes, but a
good sourcebook has flavor just spilling forth from its bindings, enough so that you get tons of ideas just reading it. A very good example of this is the Iron Kingdoms Campaign Guide; as I read it I needed to have a notebook handy because I kept writing down all the ideas it was giving me for the various locations. It doesn't have any mini-adventures in it at all, but I walked away with nearly 2 dozen adventure ideas, several of which could be combined into a campaign.
Now, I hope all of that doesn't make you think I don't like published adventures because that is opposite from the truth: I love them. I wish more games would put them out. Heck, I am subscribed to the Pathfinder Adventure Path series, as well as their module series, not because I think their world is so fantastically awesome, but because I like getting published adventures, complete with maps, NPCs, stories, etc... so that my work as a GM is made easier. (So, laziness is at the core of this for me. No surprise there.
) I am just able to see both sides of the situation. (It's a curse.)
I just wish
Shadow World* had adventure paths or module series coming out regularly, I would so subscribe!
*Enough emphasis to tell you my preferred RM setting?!?! Just in case, it is : SHADOW WORLD.