Like jkichline said, because they thought of it?
I wouldn't be surprised that engineers at Apple thought of this idea in 2006, but it's taken until 2012 for an LCD manufacturer to actually be able to gain the knowledge about touchscreens and implement it. Apple's engineers cross multiple disciplines, many more than say the engineers at LG Philips' LCD division.
The click wheel on the old ipods was developed by Apple themselves. It used a generic microcontroller part from Cypress to drive it. So it's obvious to me that Apple's been into touchscreen research years before that patent was filed.
You know how Gorilla Glass ended up as a product, right? Corning developed the glass decades ago, and shelved it. Apple got them to build manufacturing facilities and developed the techniques to cut it for mass production. It's not like Apple just sat there and Corning did all the work.
Apple used to have this sort of research in a separate group called ATG. (
http://en.wikipedia.org/wiki/Advanced_Technology_Group)
HP used to be known for a ton of research too before they split. Had it not been for shortsighted management, it had the chance to establish itself as a prime competitor in consumer digital cameras in the mid-90s.
Microsoft has their own research wing too. I know multiple people who've worked there in grad school and the stuff they do is what gets the groundwork laid out for things like Kinect to even be considered possible.