I think it is much more a matter of net worth than of income. My personal criterion is that expenses in the range of 1/10,000 (i.e. 0.01%) of one's total net worth are pretty much irrelevant.
Therefore, if you are worth 10 millions, an extra thousand dollar on top of a coach class ticket is not something you would give a second thought.

Another way to look at it is again based on the price difference between coach and business. If it is, let's say, $2,000 on a JFK-CDG passage, It feels a little silly to drop two grands on a few hours worth of more comfy seating and better food.
For that much one can go three or four times to a 3 michelin star restaurant (and eat really good food), or get a suite at an upscale hotel (and be really comfy for a day, together with your date).

As people flying biz with other people's money, that is not a question to even ask. For them it is a free ticket and I wonder who would ever choose coach, when offered a free ticket in coach, or in business.