I find it a bit strange that you would distinguish Hitchhiker's guide to the Galaxy as a comedy and not science fiction. Can't it be both? Science fiction is after all not necesarilly focused mainly on future tech, space ships etc. It can also just be a story set in a time and place where technology is more advanced than it presently is. It can be used to showcase humanity from a different perspective, or to explore a variety of social structures (Iain M. Banks' Culture series comes to mind). Sci-fi that has a specific focus on technology and science is usually called hard science fiction, at least if the hypothetical tech and science is well researched and grounded in actual, real world science.
1984 on the other hand features fantastic (for it's time) technology; mass surveilance, real time rewriting of history. Besides it is set in the future, which in my admittedly quite loose definition of Sci-fi definitly makes it at the very least halfway science fiction in and of itself.
I do agree with you about Watership Down though, because it is in no way, shape or form science fiction. I feel pretty safe putting a big, fat fantasy lable on it. And yes, the border between science fiction and fantasy is getting increasingly murky with every passing year, but not that murky!