You're missing the most important point...you're not selling the used software...you're selling the used license, or the unique license key. If I uninstall ado

You're missing the most important point...you're not selling the used software...you're selling the used license, or the unique license key. If I uninstall adobe photoshop and sell you my license key, you can install the same version and activate it using the key that I sold you. Now I cannot re-activate my copy of photoshop because my key no longer works, it's already being used by you. There's one copy of the key...it cannot be reproduced. eBooks do not require license keys to read the book. You can essentially make a copy of the ebook and send it to me and we can both read the ebook (DRM issues can be a whole 'nother post here). The only way selling an ebook would work is if they required license keys that can be transfered around but not reproduced, and that would prevent me from reading my book after I've sold my license, my rights to read the book.