Players cost more and more every level, and there's no ceiling. But the numbers can't go up forever with the same pace, it has to be slower and slower, otherwise prices would be completely rediculous. So they become more and more equal. That why, I guess.
Or maybe just to make our life harder =]
And for someone's information, just in case. Value depends on: Overall Quality, Age and so-called Talent -- hidden parameter (the pace of getting skills depends on it). The more the Value of 18 y/o player, the faster he will gain skills and SA points. Unfortunately, as has already been said, on high levels players cost more or less equal, and it becomes harder to spot a good player among slow-training trash.