My guess is that it's a healthy combination of several factors. Like YEAH! said above, I work a "salaried" job which means that I can expect to receive $X per year. Given that there are 52 weeks in a year and I am paid bi-weekly I can then expect to earn $X/26 = $N. As an example let's say I make $52,000/year. $52,000/26 = $2,000/paycheck.
So I could, theoretically, go around telling everyone I make $1,000/week and when you put it that way it makes it seem a lot smaller than $52,000/year.
So I think instead of out-and-out saying "Lionel Messi makes $20,800,000/year (which sounds outrageous) they just say "Lionel Messi makes $400k/week. That also sounds outrageous but unless you do the math out it sounds perfectly reasonable.
Add to that, Europeans are VERY particular about the cost of an event ticket. They consider, for the most part, a $40 front row ticket to be rather expensive whereas we in North America consider a $200 ticket for front row seating to be the norm.
So mostly it's a deception tactic in my mind.