I was thrown with this anomoly on the Tyros at first as well. It actually prompted me to submit a Help Request to the Yamaha tech support web site.

I wonder why Yamaha would not update the FAQ on their support website with something like this?

I now whole heartedly agree with Uncle Dave; Give us some "big boy" keys on arranger keyboards. I just purchased the Motif ES 88 and I am in love with those weighted keys. I don't care how heavy the added key weight and size make the keyboard, good keys just make my expressiveness that much better than before.