The sources inside VW said that while innovative and technically sound, the TSI forced induction engine isn't cheap to manufacture. Of course it isn't. You have to be quite blind if you don't see the complexity in the dual type forced induction engine. It has to have the engine, a turbocharger and a supercharger. Most cars have an engine and one or the other item. Having three major power making components is certainly more costly than having two components. Imagine if you make a million cars without a supercharger. The end result is that you save millions by not ordering a supercharger.
The same source also says that VW now have the technology to ensure that a single turbocharged direct injection engine may have enough punch and tractability as a Twincharged one. Of course VW will make such a statement come true. But the reality is, it all boils down to cutting costs. Cutting costs is a large fact of life these days and it is especially true with large conglomerates like VW. Let's just wait and see what happens next.
In the meantime, those of you that are thinking of getting a VW 1.4TSI Golf, Scirocco, Polo, you should go get one as you may never see such engineering innovation in a car again IF VW do decide to kill the Twincharger.