There is a huge difference. The standard was built on a 12 ga frame and the parts for it are proprietary to the standard 20 ga. with one exception. The stock and forearm are the same as a 12 ga.
Other than that parts are extremely hard to find if not impossible. You can find a limited selection of barrels seeing that they are now obsolete and no one is producing barrels (www.barrelexchange.com has some). The bolt and carrier are the hardest parts to find for it. I know guys with a reciever in the safe who have been looking for carrier parts for years.
Some people will tell you you can convert the 20 over to a 12, but I would have to say they are very talented people. I have both a 20 standard and a 12. I did a ton of research on the remington society, with gunsmiths and even took both guns apart with the idea to swap recievers and I couldn't do it, neither could any of the gunsmiths I showed them to.
Now enough of the doom and gloom. It is a heavy, I mean HEAVY duty 20. If you get it going it will last for a very long time and they shoot ohhhh sooooo smooooth mostly because of the heft of the gun with 20 ga shells. With all things even, I wouldn't sell my standard for anything in the world, but mine only had about a box put through it when it was given to me by someone who didn't know what it was.
Maybe Virginian will chime in here. He is a very knowledgable member with the 1100 and has given me some good advice in the past