Whenever an "oil" question comes up it turns into a mile long discussion and shouldn't. First of all having an engine failure do to oil is a slim to none that it would happen with today's modern oils. Something to remember is that when a VW is sold in the USA it must be happy in all 50 states from the cold north to the hot south and way over on the west coast like Arizona when summer temperature exceed 100*+ daily. So in my opinion VW specs 5w40 for this very reason to keep the engine "happy" in all 50 states. From what little I know about oil makeup is 5w40 is made from 5w base stock and additives are used to give the oil characteristics of 40w oil when hot... the key word is characteristics. Also using a 5w oil has benefits on increasing MPG ever so slightly as it requires horsepower to turn thicker oil. So if your dealer uses 5w40 or 5w30 it may be very well because where in the USA you live. Personally I have never seen an engine failure because and engine had 5w30 versus 5w40. Even with the 1.8t sludge issue it's not the oil, but the lack of regular service which causes the issue. I also think, as many others do, a turbo engine should only be filled with synthetic oil, but VW figured how many owners would pay $50-60 for an oil change? We see owners who just don't like to service their cars with regular oil changes and they are the ones having problems. Ever see a 1.8t engine inside when the owners last oil change was the free one at 20,000mile service and now the car has near 40,000miles on it! Yep, owner had to buy and engine. Personally I'm not much of a fan of 5w oils and only run 10w-30 in my cars and only switched over to synthetic about 3 years ago.
That's my oil comments.