Sugar is the main ingredient in every milk chocolate (except for the ones for people with diabetes). It's what makes milk chocolate taste like milk cocolate in the first place. Even the hardcore 99 % cocoa bitter sorts come with added sugar.
I'd like to see some people make a blind test and I would bet all the money I don't have, that they wouldn't be able to tell the difference between a 49-Cent Aldi chocolate and 2-Euro Lindt.
When they take away your other senses and your knowledge of what product you are consuming, it has some really astonishing results. I have seen farmers preferring cheap supermarket meat over their own "bio" meat in blind tests and bakermen prefer bread from a discounter over bread from a traditional craftmanship bakery.
Pride comes before the fall.
It's really not that easy and much of it comes down to ideology and what you believe. The whole wine industry for example, lives from irrationality and there is that myth about people being able to tell a wine and its year and brand only by its flavour. That is absolute rubbish. They might be lucky one day but fail the next. It is random luck.
Take away every sensation except the tongue in your mouth and strange things happen. My favourite example is the 1976
"Judgement of Paris", which marks a turning point in wine history, because it de-mystified the French wine once and for all and we wouldn't have good wine from Australia, New Zealand, Africa or South America today without it.
In essence you taste what you expect to taste. If you get a cheap slab of chocolate from the supermarket shelf, you expect nothing else than cheap chocolate and will taste cheap chocolate. I you wrap the same cheap chocolate in a fancy package, that says
"handcrafted by naked virgins at full moon", it will immediately taste better to you.