The point is more along the lines of why pay good money for a lesser quality oil, when the same money will get you top quality oil. If castrol was cheaper by degrees then you could make a choice based on price and quality, whereas castrol is priced alongside the true synthetics, so in effect the only variable is the actual quality of the product. If you really wanted to then there are many cheaper alternatives, both fully synthetic and hydrocracked synthetic which meet VW requirements, and also the much cheaper oils which vaguely claim to meet VW standards by using marketing tools such as "Blended to meet the requirements of VW504/507" or "Suitable for use where VW504/507 is required", but which are not certified by VW.
A good analogy is if you have Sainsburys supermarket fuel available (non BS fuel) at 134.9p per litre, and Esso fuel (BS certified fuel) at 134.9p per litre both within a few hundred yards of each other, would you buy the supermarket fuel because you really didn't care, or would you buy Esso because it's a better product for your money? But that's a different argument perhaps, and one which will no doubt have people calling bullsh*t again.