How is backing up an entire system different than making an ISO?

For example how is using Norton Ghost or Acronis True Image different than just creating a disk image e.g. iso? Is it really the same thing accept acompnay slapts there brand on it?

An ISO is a specific image format. Norton Ghost and Acronis True Image use their own proprietary format instead of using ISO for their image format. All three image formats do basically the same thing.

I think the ISO file is a larger file as it may not crop empty space from the backup. If I am not mistaken ISO is a bit for bit image so it stores even empty space.