While graphics make for a better cover, many of the books I have worked on are all text and graphics are of no importance.
That said, many of the current books I am working on for the near future are graphic intensive. Some have just ornate drop caps at the start of chapters while others are a tight combination of text and graphics. One, A Child's Garden of Verses, has many graphics that need to fit together tightly to produce the finished pages. (Even html2lrf is having trouble with this at the moment even when autorotate is turned off.) Others like the Beatrix Potter series are simply alternating text and graphics without any side-by-side of text and graphics.
So yes, the integration of graphics is a big deal for any tool that is used to produce LRF books.