While it's the same "oat", and you get the same basic nutrients, steel cut oats are less processed. You preserve a bit more fiber and the overall product is a bit more fibrous and filling. It is similar to the difference between "hay cubes" and just plain hay for horses. Even if you cube up the same exact hay you'd feed in a round bale to the horses, they will process the hay cubes a bit differently, simply because they are already more processed.

That's not to say that the difference is that big a deal. Unless you have a low fiber intake, digestive problems, or a desire to feel more full for longer, there is no substantial health benefit of steel-cut oats over oat meal. But as far as fiber is concerned, they do have a bit more unprocessed fiber. Again, not a big nutritive difference (if you looked at the nutrition label), but your system will treat steel cut oats as if they had more fiber. Do you get what I mean? I have a feeling I'm not expressing it very well.