I'm kind of copping out a bit here, but this is more of an overarching comment before I get into specifics: Images was not a big departure from WDADU in terms of writing. They were a band that was still finding themselves, and obviously finding a new singer, when they wrote and put out I&W. But stylistically, I don't hear a big departure from WDADU to Images--just a maturity and natural growth. But to me, there is a big contrast from there going forward from one album to the next from I&W through TOT. To me, each of these albums sounded VERY different than what had come before. And Octavarium sounded very different than its immediate predecessor, but didn't sound that different than what the band had done throughout its history. With the exception of The Astonishing, I don't feel like any albums from Octavarium through the last album are as drastically different as other things they have done in their career. Those later albums just sound like natural outgrowths of what they developed earlier in their careers. Yes, there are individual songs (or even groups of songs) and individual parts that are new and "experimental" (for them), but no single album feels like as big a leap in a new direction as each of the new albums did back in the early days. And I'm not saying the band has gotten stale, or predictable, or less creative, or has run out of things to say later in their career--far from it. I think it's a combination of factors. First off, when there was less of a body of work to compare to, I think those big leaps from album to album seemed a lot bigger than farther outside the box than now, with such a large body of work on the table and a much "bigger box," comparatively speaking. I think it's much harder for any newness to feel like as big a leap in a new direction when they have such a huge and diverse body of work to compare it to. Second, I think it's also a factor of them just having found a broad array of what works well for what they want to do.
Anyhow, I know that doesn't directly answer the question, but those were the thoughts that immediately came to mind.