This is more like a discussion about business strategy and efficiency.
It would be a disaster if business people don't try to understand designers, especially if they decide to not let them use their full potential to reflect and have their say in every decision making regarding deliverables. Professional designers are aware of that everything they produce will not be used or taking into business. It might be frustrating sometimes but its something we deal with everyday just like business people, directors etc. have to take decisions they are not always comfortable with. Most times there is no budget for perfect designs.
However, I can tell you that this discussion is about delight. Remember this word, "delight", its one of the ingredients in success for many game changing companies. As been mentioned here by others, but in other words from me; pixel perfection means quality and . This is what makes people feel a WOW-factor around your products and brand.
Delight is more or less needed to be successful in IT-business today. Paying attention to this makes you standout better. Even the smallest of details can make you grow in right direction. Most of times startups are better of understanding this because they need really much "delight" to get into running their own business. Startups greatest weapon is delight.
Its not always efficient to pay attention to every detail but if everything in your product have this proof of delight in itself.. Then I'm very sure you will be payed right or even more than you expected for your product. Delight makes a lot of difference in how much costumers are willing to pay for your product just to feel and enjoy it all. That's the underlying answer to why delight pays off. It makes you sell more in the end.
Delight is most of times needed when there is an emerging market, new market or when a company need to showoff their product to steal market from other businesses. But if you are alone, or have few competitors, and have great business idea that solve a need in a good way for its users.. you might not need to pay as much attention to delight. You will probably not struggle with the competition.
Delight can also be awesome animations and good workflow. So don't stare blind at "design" as eye candy only. Design is also the feeling while using the product. This is what professional designers are great at achieving. Now we reached what UX turns out to be today and by here I stop writing. I just wanted to fill in what I think is the connection between design & business.