This is somewhat true, Motrax.
As I referred to Rachmaninoff in another thread by the word "primitive", somebody (ayahav?) corrected me (excuse the limitations my self-expression faces in form of English vocabulary) that the better expression to use would be that the music communicates to our primal instincts. When I listen to Rachmaninoff, the music draws pictures in my mind, it doesn't even ask me how do I feel, it just takes the role of a teacher and shows me this imagery (I am a "visual listener") of life and it's fascinating phenomenas. It is so emotional that its hard to rationalize, unlike for example Prokofiev's modernistic works (I've written an essay on Prokofiev's Toccata and my high school teacher gave it an "F" cause he was sure I had ripped it from the Internet

). These are probably the same things that you described with words "being human", therefore close to our ´´hearts´´ and being "naturally" playable.
Also, "linear" is a good word for Moonlight Sonata's 3rd movement, when compared to the Prelude. Rachmaninoff's rhythmic progression is more free-form-like, while the Moonlight has a predictable note for almost every sixteenth throughout the score.
On the other hand, what is difficult about Rachmaninoff's expressively "trivial" music, is that if you don't have the emotional charge that it takes, the music can also sound very ugly. Its like an exceptionally good piano: it has the potential to sound superb but if you don't have the ability to play real well, the beautiful sound of the piano and the broken fluency in handling it create a contrast that serves neither.