Doesn't matter if the original user uninstalls the program or not, once they register they key, that's it. As far as them trying to eliminate the resale of modern PC games, keys have been around for forever. Steam was just a twinkle in Gabe's eye when they introduced CD-Keys. It seems in the last decade they've ramped up the need to register the keys online though.
Steam it seems is more of a blessing than a curse as companies are releasing their back library of titles on there. It's MUCH easier getting the download for Loom off of there than it is to hunt down a copy in the wild and hoping it'll work correctly on my setup. That's not to say you can't find PC games in the wild, it's just they're not as common as their console cousins. There's been a decent amount of great finds in the Dec/Jan finds in the What's It Worth forum lately.