They may spec them for free, but eventually they expect to get paid or laid. My guess is that:
See post #9. Someone doing it to get laid really, really doesn’t understand how the business works.
Now, if the expect to get screwed, it is a different story.
My understanding is that studios return scripts unopened for fear of getting sued by some idiot who claims they stole his idea - even and especially if the idea is in every other script they see.
I also understood that if you want a script to get looked at, you get yourself an agent. If you can’t convince an agent that your stuff might be good enough to sell, when he isn’t paying any money for it, you would have a real hard time convincing a producer.
JMS had to temporarily scrap a whole plot arc for Babylon 5 because somebody posted their identical story idea on the B5 message board. It took quite a while for them to finally get Legal to get the guy to sign off his rights to the outline. He said ok immediately when asked, but it still botched things up.
This description fails to recognize how the areas of production (pre- and post-, too) are compartmentalized and one advances on tracks which don’t often crisscross.
This step is unnecessary, and generally is skipped. It’s cheaper and faster to hang out with enough of the right people until you can go directly to 2). Contrary to popular belief, there’s nothing you get in film school that you need to get the “crappy job in the industry.” Making a short film in film school won’t do a thing toward getting you into the creative side of the actual industry. No producer cares if you took a whole year to make a 20-minute film with your parents’ money. Those successful people in film who have gone to film school succeeded because of their drive, not because of anything they got in film school that couldn’t have been gotten elsewhere (a lot more cheaply)–and that includes connections or contacts.
This is also a widely-held misconception. There is no organic arc between the crappy job and writing screenplays. If you are a good PA, then certainly you’ll get noticed, because there is such a large pool of blithering, incompetent fools starting off this way, who actually believe in this idea of the arc, and just want to be “in the industry.” What will happen is that you work your way up, and if you work well, you will become a script supervisor or a an actual AP. At this point, you’re making so much money you won’t bother to try script writing, and even if you do, the fact that you started with the crappy job as an assistant makes no difference whatsoever. It might give you access, and that’s it. Generally the people who can actually become good at being an AP aren’t scriptwriting types anyway. APs and script supervisors are like organizational efficiency and control experts–not creative types. (The personal assistant thing is more out of a Hollywood plot than actual Hollywood practice.) 
Sorry. Don’t count on it.
Most people don’t realize how careers in the industry move along tracks that you get locked into. I started doing sound work with the “crappy job” thing, and then ended up doing boom, and assisting with mixing. The best I could have hoped for would have been becoming a full-fledged mixer, in the union. And if that had happened, I’d be making a lot more money now than I do in education, but that wouldn’t get me any closer to writing scripts, or becoming a DP or directing or whatever.
You have to realize that there are thousands of people involved in a production, and that most of this work has nothing to do with creativity or crafting good, marketable narratives for screen. They’ve got those jobs because they’re good at doing something that involves a completely different skill-set. If producers read every script by every production assistant who wanted to be script writing they’d go crazy.
My daughter acted in 3 NYU student films (at the Masters level) and none of the students we met went to undergraduate film programs. In fact, the consensus was that this was a very bad idea.
I agree with your point about drive, but that is true of anyone today, not just film students.
Well, those crappy jobs are entry-level, just as in any other kind industry, so you’re right, it’s not just film students. Whatever work a person does, drive and determination are most important to advancement. In movie production, you learn on the job what you need to learn to move up. If you want to get called back to a set (and paid more), you just do a good job. There are so many idiots that are trying to get into the movie industry who are incompetent (or don’t really want to work–they just like the idea of being “in the industry”), you’ll stand out if you do a good job. But if you start off in set design, for example, you’ll most likely stay in set design, even if you work you way up to the highest spot in that area of production. Few producers or directors are interested in reading a script that even the head set designer hands them.