Actually, Yamaha makes many arrangers with more than 61 keys...just not TOTL...the DGX/YPG are excellent products...and the bane of Roland's E-60, from what I have heard.
Well, big difference is the YPG's sound like toys compared to the E60's professionall sound..
But then to many people are blinded by the sign "Yamaha". The YPG 635 is rated just under the S500 when you look at the sounds. (thats where yamaha places them)
While E50/E60 are direct contenders of the S900.