This is so very true, and a real paradox for those bands who are living this reality because often the finished product isn't what came out of the studio and that makes it not what your die hard fans want to hear. This would be a bigger problem early on. Once you've toured that material a few times, it's easier to get away with changing it.Another thing to consider.... when bands are recording, they are under a lot of pressure to get the work done. There are time constraints, and artistic limits put on them by producers/executives. There is a good chance that the band doesn't even consider the song "done" when they leave the studio.
Now when they are on tour they have spent a lot more time with the song. They rehearse like crazy... often what you hear on the road is closer to a finished product that what you get on the album.