Okay, so you collect for reference (and just because you happen to like "Progress in Optics Volume VI").
That's not a "what the hey" reason, you have a legitimate reason to collect those texts.
Even a music downloader who collects gigabytes of music they may never listen to, generally limits their collection to the genre of music they prefer, as evidenced by the fact that the majority of music downloaded and/or pirated has been collected by young people, and the majority of the legit and illegit content out there is the popular music (mostly rock and R&B) favored by those same young people. And with books, where the news is filled with
Harry Potter pirates, but noticeably absent of
Mike Hammer pirates.
That's something to think about in terms of e-books, because if you can create a system that the young people (who tend to be the early-adopters) will accept, it will have to be with content they want (or need). You can thereby establish a model with them, and once it is successful, expand it to encompass other genres. (That could even be why pubs aren't rushing to bring old content to e-books, as they don't expect young early adopters to want it. Maybe.)