Originally Posted by mimartin
Can't speak for the rest (don't have them), but with Steam, you just redownload them. It is just like magic or having the disc, only you can't lose the disc or scratch it up.
And with Steam, you have to hope someone doesn't hack your account or you don't get banned for some reason... I know cases where people were banned without doing anything wrong. And they don't give any explanation.
That's the problem of being dependable of 3rd party software or servers. You don't have any control over what you legally payed for. On GOG for example, you do have your account where you can download the games you legally bought any time you want. But if you choose to download the .exe and save it on a disc, hard drive, whatever, you can. And you won't ever need any kind of activation or login to play the game. It yours.