When I bought my 814ce in November, i played it against a D-18 and a Songwriter Deluxe. All very nice guitars in about the same price range. I narrowed ny choice to between the Taylor and the Gibson. I assume the Taylor had the Elixer NW 80/20's on it and I'm not sure what the Gibson was sporting. Regardless, to me and my friend who came with me to offer a second opinion, the strings on both guitars sounded dead and the shop restrung them both with strings of my choice - D'Addario PB lights, which I have been using happily for years. I recently made my first string change and am now playing my Taylor with Elixer NW 80/20's for a bout two weeks now. The jury is still out, but so far I prefer the D'Addario PB's.
To the original question, I have also heard, as has been previously mentioned, that Taylor uses the Elixer NW 80/20's for shelf-life while the guitar is hanging on the wall. In my case it didn't seem to work, and to michaelw's point, they probably use them because they generally last a long time, sound good, are inexpensive, and anticipate that the buyer will likely change them when he/she gets home.
I also think cost is a major factor in this decision. When in mass production, every penny saved goes directly to the bottom line.
Jim