PSR Tutorial is a Yamaha fan persons forum and if you put a Yamaha badge on a cheap Casio they would defend it to the hilt no matter how bad it was, so using this as a benchmark as to how good a Genos is, means absolutely nothing. (Mention any other keyboard and you are held in disdain unless you are slagging it off)
AS to SZ, out of the minuscule amount of arrangers that are purchased in the US (SZ is mainly US centric) the largest majority are Yamaha or Korg these days, so these will show up the most.