You are right that users think they are better off without files. And I completely agree with you that web applications provide a nice avenue to a life with no files (No access to the local filesystem from within the browser? Great! We'll just store everything in a database on the server).
But then we start to have these situations with data lock in that are definitely bad for users. Take Facebook since it's oh-so-popular to bash them these days. If my Facebook data were stored in an encapsulated and portable format I'd just go to a new social network that respected my privacy and say, here's my data, ready to go. Import it.
Now it may be the case that most users are willing to turn over their data to the application that created it in exchange for simplicity and ease of use. But I don't think that's a debate that many users are having with themselves right now.
"Facebook would be better if Facebook used files" is a bit of a strawman. [Edit: No, it isn't. Crikey, failing at English: what is the word for an argument premised on a proposition that is contrary to fact? It can't just be "wrong", that's what 3rd graders say -- needs more Latin.]
Do you know a single application that abstracts away as much data as Facebook does as files? Anything on my computer nearly that complex, like an email inbox, a photo collection, or my iTunes stuff exists as an opaque blob with a proprietary reader. (In the case of my inbox, it is an opaque blob with widespread inport/export capability into opaque blobs of different colors.)
It has a file on disk like MySQL does: OK, technically accurate, but I'm not capable of actually doing any of my usual file activities with that file.
That is aside from the "whose data are we talking about, anyhow" conundrum. Probably 80% of my presence on Facebook "belongs" to other people. Tagged in a photo taken by my mother of my brother's wedding: think quick, is that in my export or not? (For that matter, is my brother in my export? I'd kind of like to import him into my new social network. You can do that, right? Oh and Farmville.)
If Facebook doesn't work for you (and I agree that it is very complicated, so maybe not the best example), then choose another popular web application. My point was not that Facebook would be better if it used files, and I think you know that. My point was that abstracting away from files makes data lock-in very very easy. And that users are probably not well-informed enough to make a good decision about trading off usability with portability.
I think you can have your cake and eat it too. A webapp that's task centric can still offer export and import features for power users. You are right that if people stop asking then such a feature might not be provided but at least for now it seems to be more of policy decision on the company part than a hard and fast numbers game.
But then we start to have these situations with data lock in that are definitely bad for users. Take Facebook since it's oh-so-popular to bash them these days. If my Facebook data were stored in an encapsulated and portable format I'd just go to a new social network that respected my privacy and say, here's my data, ready to go. Import it.
Now it may be the case that most users are willing to turn over their data to the application that created it in exchange for simplicity and ease of use. But I don't think that's a debate that many users are having with themselves right now.