You're right. It is very possible that they are in violation of the GPL. In fact, unless all the tools they're using are licensed under the lesser GPL, anytime they link to a GPLed library they must disclose their source code.
On Nov 9, 2006, at 1:20 PM, James Fry wrote:
However, Yamaha do have an obligation to give customers the source code
for the portions of GPL code they have modified. Looking at the
disklavier update, there are modifications of the distribution they have
used, but I haven't looked further to see if there are additions to the
kernel or other software present.