Remember the same thing when create styles at Technics as well, I think I did read it somewhere in manuals, as well as been told that it had to be done in the key of C to work properly.
I got the impression that this is common at all brands to make it sound and work right both in major and minor when play whatever key as we usually do when use the styles.
Of course it's possible to make parts in other keys for use as sequenses or composerparts etc. I had, or maybe still have some styles where intro and endings etc. is created in other keys, but then you have to play in the key it's created, or else it did not sound any good at all.