Given that Apple seems to have some expertise with construction glass (see the Apple Stores) it would make a certain amount of sense. However, look at Corning's whole profile. Ceramic Substrates, Diesel Particulate Filters, Fiber Optics, Fluoride Crystals, Custom Materials. If you are good at consumer electronics, why in the world would you want to dive into material science and chemistry?
In fact, look at the food processing industry. It seems someone is always buying one product line or another, mining the profit out of it, mismanaging it, then selling it to someone else. It's not that they have a speciality or interest in, oh say peanuts or ice cream. It's the fact that brand is making money.
Personally, I think Apple has been very wise with their acquisitions. Over-reach is the one thing you want to avoid.