I think you nailed it. Clarke's dialogue in his script was mostly removed. Relevant passage is this: "Close to tears, he left at the intermission, having wat

I think you nailed it. Clarke's dialogue in his script was mostly removed. Relevant passage is this: "Close to tears, he left at the intermission, having watched an 11-minute sequence in which an astronaut did nothing but jog around the centrifuge in a scene intended to show the boredom of space travel. This scene was considerably cut in the version put out on general release. If Arthur was disappointed by Kubrick’s decision to cut his dialogue and narrative to the bone, he was eventually reconciled by being able to put everything left out of the film into the novel, meaning that each man was able to produce his own preferred version. The success of the film ensured that the book became a bestseller, as audiences sought answers to questions raised by Kubrick’s version, and Arthur soon got over his disappointment, going on to write three bestselling sequels to his novel, only one of which has been filmed so far."