Brake rebuild.. i guess it depend what they mean.
I have posted already that on my just over 3 year old bike, with under 10k on the clock, that I have already had to strip front and rear brakes due to dirt build up causing noise and grabbing.
I did not have to go as far as taking the calipers or master cylinders apart to change seals, but I did have to strip the pads and carrier sliders fully. I also had to remove the front brake lever to lube its pivot point, and also remove the boot on the front master cyl to put some lube in there. It was also noticible that all the fasteners on the front and rear calipers had copper-slip on them, so it was clearly not the first time thay had been apart.
Last time I did it was about 6 months ago, and the front brakes are just starting to grab again.
From prior experience of owning a bike, regular servicing of the brakes is normal. I had to adjust the front shoes and cable on my CD200 monthly, and on my GSX250 it was weekly.
Ask them what they mean, exactly, by a rebuild.