True, maybe we're using different definitions of "entertainment". I guess unlike you, I find the parts with actual gameplay more entertaining in a speedrun than the cutscenes. That's what separates speedruns from regular playthroughs--the focus is more on the gameplay than the story.
You're right, I got away from what you were saying. However, I can testify that after having watched a cutscene for the 100th or so time, a runner isn't always worried about doing the most entertaining thing. And yes, sometimes they may end up doing something that is really annoying to watch. The thing with speedruns is that you don't know ahead of time which attempt will be successful, and it can get tiresome doing the same thing--the most entertaining thing--every single time.
I haven't posted much on these forums, but I'm a regular at SDA. I have to disagree with Warp--I don't think that the whole point of a speedrun is entertainment. Sure, entertainment is important (and nice for the viewer as well), but it doesn't take precedence over speed. An example from the game I'm most familiar with: In the runs for Final Fantasy 3/6 (both the TAS and my run on SDA), for at least half the game most bosses are killed with Joker Doom (an instead death attack). It's not that entertaining to watch over and over again--it would be much more entertaining and creative to find other ways to kill things--but it's the fastest, and no runner is going to sacrifice more time when it's so easy to do. Maybe this doesn't address your point, since you were talking more about graphics and cutscenes, but my point is that entertainment is not more important than speed in every case.
As for segmented and single-segment runs: I have completed runs of both types (admittedly they were RPGs, so my experience is limited in this area), and I'd say that both types take a lot of work. In an SS run, you have to be good at the entire game all at once and be able to concentrate for longer periods of time, but more perfection is expected in a segmented run. I'll stay out of the debate over which is faster, though, because I don't have enough experience with other types of games.