Hi Vadim
It depends how you approach the Arranger Keyboard, you can either choose the style and then choose a song to match, (As you say playing like the manufacture wants you to, and which is great for starting off in music) or choose a song and then find a style that gives a good match, (The player makes the decisions not the manufacture, which is great once you have gained experience) and then modifying the style to suit. (If required)
Rock Music is Primary Guitars, but keyboards are also featured (Particularly Organs) a lot in the background.
Another way to look at things

Bill