You guys are both right. It IS a better example of truly "fragmenting" a song. But it was indeed done for a legitimate creative reason. In hindsight, I wish they would have left it together. But I still absolutely respect the creative decision and the reasoning behind it. As an aside, I think another factor in addition to it being a good opener and a good closer, I also think they just felt like having a 20+ minute epic to close out an album right after doing that with Octavarium would have been too formulaic. Splitting the song solved that problem as well. So many years after the fact, if they closed the album with it, it would probably just be a little footnote by now. But at the time, I can see how it might have been a sticking point and made them want to rearrange the album. And they would have had the same issue when they got to BCSL. Not having the giant epic close the album solves that.
Of course, they could have gotten around it simply by having another song be the closer. In my alternate track listing for that album (the only time I have rearranged a DT album), I have the entire epic start the album, and I close it with TMOLS (I don't like the song, but it seems to work better as a closer). I really like the flow of the album that way. To a new fan, especially one who might not be a prog fan, asking them to sit through a 25+ minute piece of music to start off the album is a big ask though, so I get why they might not have chosen to go that route as well. But it certainly does flow well.