A new piece of medical equipment is being tested right now called the Pedisedate. Basically, it is a headset that is placed on a child before they are admitted to surgery. The device connects to a Game Boy or portable CD player (yup, not a Nintendo DS or iPod — apparently the Pedisedate also transports you to 1996) and a snorkel-like piece swings forward and is placed over the child’s nose. As the kid plays videogames or listens to music, nitrous oxide, an anesthetic gas, is emitted through the snorkel and puts the child to sleep.
It’s probably more that a DS wouldn’t be allowed in the room for to it’s wireless communications and not for having reasons just for pollution of the radiowaves in the area. So a Gameboy sufficed and Nintendo at the time probably had a load of stock in a warehouse that they could donate.
As if Nintendo would donate anything. The probable reason for using a Gameboy instead of a DS is that Nintendo wanted too much for licencing the use of the DS.