As with anything in the real world there is always a "yes but" and "it depends". 10k hours succeeded because it is generally the right idea. It's not a mathematical rule. Some common sense is still required. You can't stop people interpreting it to hear only what they want to hear.
If people would actual read the book Peak they'd understand that it isn't even about those 10k hours.
What Ericsson says is that what creates peak performance is studying just beyond the edge of your comfort zone with (as much) personal feedback (as possible) from an experienced mentor; so not just playing around a bit by yourself.
For quite a few fields 'expert' levels happen to come down to about 10k hours of such practice, which is where the number comes from, but he also warns that you will need increasingly more than that to rise to the top as more people put in more hours.
