Yes, a laptop really is a musical instrument, or can be if you add the right software and a couple of hardware peripherals. A laptop orchestra, though? Check it out over at Peter Kirn’s Create Digital Music site.
What concerns me about the ensemble shown in the video is not the concept of using a bunch of laptops in an ensemble. No, what concerns me is using the Wii as a musical instrument for gesture-sensing purposes. As a cellist, I expect that a musical instrument will provide accurate sensing of tiny muscle movements. That’s what playing a musical instrument is all about!
Trying to play music with a Wii strikes me as being a lot like painting a picture using a roller.