then buy this

Seconded.

Bought The Lunar Pack. Can't wait.

The difference is, they're telling you straight out "We will give you more activations, no questions asked." Also, they usually just give someone a brand new serial key and let them re-activate it all over again...there's no "Wait while we ask the publisher..."

Pretty sure the manual says that as well, it just doesn't feel the need to sell you on a basic feature. It is like buying a car and being thankful that the dealer said "You can use this to go grocery shopping" :p
And if they are giving out brand new serial keys, they are recycling keys, which is actually BAD. Imagine for a moment that someone got a new key "no questions asked". Then they have two serials, and might very well use both. Then, when you buy the game, you get the key they returned. Bam, you don't own your game.

No, but I also don't expect them to issue new keys whenever someone sends them an email. That costs money.

It might depend on what their deal with the publisher is. If they are a trusted store then perhaps the publisher might give them an unlimited amount of keys (since they keys themselves don't cost anything), but allow them to only charge money for the ones that go towards new purchases.

Possible, but highly unlikely on the simple grounds that someone could EASILY get spare keys for their buddies (defeating the purpose of DRM :p).

Not everyone is a thieving asshole.
Also, I guess if one keeps "losing" them, I am sure there are plans for that.

Not if by getting a new key your old one gets deactivated. I have no idea if this is how any of it works, but it seems like it would be a simple thing to do. The publisher gives the store an unlimited amount of keys. The amount of keys they use should be equal to the amount of purchases plus the amount of keys they "send back" to be deactivated.
Or maybe not, it's just a guess.

It is definitely something I find interesting (them refunding activations by calling Securom/Starforce/TAGES still seems more likely, but whatever).
For something like Steam-based games, disabling keys is easy. But what about the activation-model games? Theoretically, said keys could be disabled by calling up Securom/Safedisc/Tages, but if you are going to call them anyway...

If the store does have to contact the publisher or one of the DRM companies who's so say they have to sit there on the phone for each key? Perhaps there is some sort of "business" method that allows them to send in re-activation requests in bulk. It's either the company deciding what is a valid request or trusting the store to decide instead.

The important point here, is that when GG do it for you, you don't get said publisher/DRM support accusing you of being a pirate simply because you used all your activations. I'd far rather deal with GG than EA support for example, when it comes to asking for activation limit resets.

Please, make use of it:
http://www.gog.com/en/forum/general/steam_impulse_whatever_else_your_heart_desire_bashing