Looks like a great number, but remember that many are on their second one after their first one failed for some reason. It means only one sale for two touches in those cases. I don't know what pecentage are replaced under warranty, but any percent is significant. Of 5 people I know with Touches, two are using repacements. Not a scientific sample, but if you extrapolate that 20% to 13 million it means only 10.4 million out there are still working. Some of the defective were surely resold as refurbs after being repaired, but that's another unknown number. Just fleshing out the significance.
What to do about it? Write an iPhone/Touch app that every iPhone/Touch owner wants. Charge them $1.43 each, and however much money you make (before taxes) will give you a useful number for how many are out there and working. Make 20 million dollars? That means 20 million iPhone or Touch owners bought your app. It also means you can quit your day job. 😉