Every keyboard has its own personality, so to speak, and this -in the case of arranger keyboards- is determined by both the sounds and the styles.
So, different keyboards strike different chords inside different musicians: when I owned an SD1 (like DonM has now) I was inspired to record songs like "Guajira", "Hold on, I'm coming", "Sweet home Chicago", "When a man loves a woman".... because the SD1 is strong in the R&B, Pop, Country and Light Rock department. Unfortunately, it didn't inspire me to play a lot of jazz or latin stuff, because the styles were dull or too "heavy" and the sounds lacked the sparkle needed to play that kind of music.
Now I own a Tyros and I think I can say that it's the keyboard that inspires me to play the music I like most; should I buy a different keyboard, I would both regret the Tyros and at the same time had to "redirect" my inspiration according to the tools I'd have at my disposal.
All in all, I can perfectly understand why Don Mason likes the SD1 so much: simply told, it's the best keyboard for the kind of music he likes most.
Don, when will you post a few songs recorded with your new baby?