As others have mentioned, traditionally the 3 digit rifles have been the long action rifles while the 2 digit have been the short action. As an example, I have a Savage 10 in .308 whereas if it were a .30-06 by traditional standards it would be a 110 since it would require the long action. Basically, if it was a long action you tossed a 1 in front of the model number to make it 3 digits. Now, that nomenclature seems to be messier now so I'm not sure how much that holds up any more.
The other thing I've read is that the 11/111 Series has tended towards hunting (sporter type barrels, etc.) while the 10/110 series has been slotted to fill the Tactical/Law Enforcement role (heavier barrels, etc.). IIRC, the base action is the same but it's the other features that distinguish them. At one time I think the 10 denoted a detachable mag but that has definitely gone by the wayside as plenty of 11s now come with them.
I've also read over on Savage Shooters that there are 3 different accutriggers: Standard (2.5-6 lbs), Varmint (1.5-5 lbs) and Target (6oz-2lbs). My 10 allegedly goes down to 1.5 according to the listing but I haven't messed with it yet, so it might have the Varmint trigger? That may be a difference too but I don't know.
So, I guess it comes down to it's kind of a crapshoot and they've made a mess of their nomenclature. It definitely can make it a pain to get the right aftermarket stock, although I did a crap ton of research and got the right one on my first attempt.