BioShock used to have a ridiculous system that essentially limited the number of installs to two per disc unless you were prepared to go through some of the most stupid nonsense recorded in PC gaming history. Online activation remains mandatory (EDIT: okay, maybe not), but at least the number of installs is now unlimited.

Warcraft 3 and Starcraft, since you mentioned Diablo 2.

It's perhaps worth noting that even the Steam version of Far Cry 2 is DRM-free. So if there's a sale on and you're interested then there's no reason not to buy it through Steam.

So, is it mandatory, or not ?

Oh yeah. That reminds me. A lot of THQ games have gone DRM-free. Dawn of War 1 (and expandalones) have. I can't remember which others have off the top of my head. But there's more.

... Doesn't Diablo II have Battle.net DRM?

Doesn't matter. The game's still not DRM-free by any margin and you'd need the Steam version to avoid installing the really fucking nasty malware* it comes wrapped in, regardless of what the patches may disable. Remember that SecuROM is near impossible to remove without a format, which makes some of those earlier, really bloody nasty incarnations the kind of thing you don't want to let near your system, no matter what.

*Yes, it is malware.
My disc copy certainly doesn't. Never once in my life installed Battle.net.

Diablo 2 (the older versions at least) works like Starcraft 1... it doesn't *require* Battle.net, but that's how you get game updates... but once the game's been updated there's no need for it anymore. If you can find an alternative source for patches there's no need for it even for the first time.

Never got into the details with it, I just don't like when I have to be online to play the game / I have to activate the game.

I don't think anyone does, really. I guess it's just a matter of how much crap people are willing to go through over an entertainment product.

Apparently, it is. The number of activations is unlimited, but still.