Interesting points you make Kumabjorn
I've owned an ereader for 2 years now (Sony 650), and my purchase of hard copy books is about the same level as prior to the purchase and they consist of non-fiction.
However, my fiction book list has increased by maybe 300 because of all the freebies (Amazon, Kobo, Sony).
Yep - I've made some non-fiction and fiction ebook purchases (only using vouchers) and they may number 20.
So - the purchase of ereader devices has worked out financially beneficial for me.