uhm no it doesn't, it restores to the latest firmware thats out at the time of the restore. you can download different firmware from other sites and then use shift+click restore and select the firmware you downloaded but i have never heard of someone downgrading from 3.0 back down to 2.0. sorry but your stuck at 3.0. why would you want to downgrade anyway? 3.x series of firmware can be jailbroken.
Downgrading is very much possible. The hardest part is finding the files you need to do the job. Downgrading from 4.0.1 to say 3.1.2 is achievable. I did it because 4.0.1 had issues with cydia's apps. There are now a lot more compatible apps/tweaks for the 4.0.1 firmware.
The files that you need to downgrade are:
* " LibUSB64 "
* " iH8sn0w - iREB V3.1.2 for windows"
I am running a 64bit system so these files work for that.
If you have problems finding the files let me know and I will sort something out. Google was my friend that's how I found them.