Good morning! As mentioned in my PM to you, there is no running promotion by GamersGate for The Sims 3 & its expansions at this very moment.

I've check the price list in YouBeli.com plus TSB & found that they're a lot cheaper compared to the GamersGate price. You might want to take a look:
YouBeli.com price list for the Sims 3 & expansions.
TSB price list for the Sims 3 & expansions.

Aye aye! I'll send you a PM if I happen to stumble upon any promotion for The Sims 3 series.

Steam is not the cheapest all the time. That is why I also provide service for the other digital game distributors.
Ahh... unfortunately, that link is only applicable to those living in the United States. Kinda weird that there's a sudden demand for the Sims 3 series though.

As what we've corresponded via PM, I'll inform you if there is any discount for the Mac version of The Sims 3 by any of the digital distribution platforms.

Unfortunately, no. You'll have to create an account for each distributor & the game will still be sent to your account as a gift, exactly the same way how Steam gifting works. As such, the CD-key that comes along with your game is safe & secured from prying eyes, including the person who sent you the game in the first place (that would be me).

The minor differences between Steam & the other distributors are:

1. Steam requires you to install & log into the client to play your Steam games. The other distributors are client-free hence no login is necessary unless required by some games with DRM.
2. Steam games can be played right away once the download is completed. Games from the other distributors are almost similar to the standard installation process where you'll have to specify the installation directory, click on multiple I Agree & Next buttons before you can play the games.

If you were to ask me, there are 2 factors that influence my decision on which platform I'll be getting my games from.

1. Price. Some games are cheaper in Steam while some other games might be cheaper in GOG. The same applies to Direct2Drive & GamersGate as well.
2. Availability. Steam requires you to login therefore Internet connection is a must. Of course there's the Steam Offline Mode but to make it much simpler, I usually get games from the non-Steam distributors if the games do not have multiplayer capability.

Do let me know if there's anything I need elaborate further on ya?

Erm... yes, you can do so but there are conditions to be met.

1. You'll need to register her a GamersGate account (let's say we're getting The Sims 3 from GamersGate) first.
2. You can then download the installation files & burn them into DVDs.
3. She'll need to transfer all the files into a folder in her computer & initiate the installation.
4. To get the installation started, she'll need to enter the username & password which you've created in step #1 above. This means that she'll have to stick with that account name forever since the game is now tied to that account.
5. In the event she need to reinstall the game into another computer (or reformat her computer) but lost the DVD, she can access the GamersGate website, login using the same credentials as mentioned in step #1 & redownload all the installation files again.

Yup, the login is only required during installation to authenticate you (or your friend) as the rightful owner & at the same time, prevent piracy.

Wow! You're still up at this ungodly hour eh?

Well, the thing is, game developers / publishers are still in the stage where they're trying out various methods to combat piracy. Prior to The Sims 3, Spore had SecuROM implemented & this didn't go well with majority of the gamers out there. If you're interested, here's a short excerpt related to Spore & SecuROM that you can go through in just a minute or two: http://en.wikipedia.org/wiki/SecuROM#Spore

Back to The Sims 3, my point is, you may install the game into multiple computers but at the end of the day, it kinda defeat the purpose of buying the original copy of the game in the first place, right?

Ooh... sounds like someone special to you eh?
I've sent GamersGate a tweet 2 days ago but still no reply from them. Still in holiday mood, perhaps.