That's the point, lee.
There isn't a single keyboard out there with sufficient CLEAN power output and SPL to keep up with a live drummer (with NO monitor!), let alone a whole band. If you are performing at a club level or higher, you can't use the speakers (and probably shut them off for fear of blowing them).
But there are a LOT of players here that play low level cocktail gigs, NH gigs, tiny senior citizen parties where playing at club level would get you fired! However, most of these STILL use a PA... To be honest, I have yet to hear a portable arranger with a sound system good enough to sound clean on simply the piano patch at the same volume a REAL piano can do.
Add to that that even a POS home theater system completely blows the arranger's speakers away for fullness of range and volume, and costs little, I have to start to question exactly what the purpose of the speakers are at all...
And all I can come up with is the 'home' user who is too cheap or too ignorant of what his arranger can REALLY sound like to buy a decent monitoring rig. The kids don't want to haul around a Logitech system from bedroom to bedroom, and it complicates putting it away in the closet (where it remains from week to week)
But other than a practice tool for a 'pro' user, when quality doesn't matter, I really don't see the point in them. I've seen Mike McDonald on his Yamaha, in fact, I watched him and Christopher Cross personally hump the damn thing back to his car (it was a small local songwriters event - mind you it just goes to show, no matter how big you get, NO-ONE wants to move your piano at the end of the day
), but I know for a fact those speakers weren't on during the show...
For me, the extra weight of speakers, as poor a quality as they are, is not a sufficient incentive to restrict my choices to ONLY speakered models. I'd rather use a decent set of cans if I HAVE to work on it while it's not hooked up. At least there, I am getting high quality sound...