I have to agree with you on that one.  You're right too.. Casio had them on the MZ-2000.. Even though there were like only 15 of them, it was still a nice addition.  I'm surprised they're not showing up more in arrangers too.  I remember the original DJX had some as well.  You can do some pretty wild stuff with them if you know how to program.  I sure did love the ones on my old Roland XP-60  

Squeak
 
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GEAR:  Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller).  SOFTWARE:  Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.