No seamstress did not make wages in the top 10% in the richest country on earth while working 7 hour days.
The seamstresses in the story lived in the richest country in the world (at the time!) And at that time inequality in GB was so eye popping that these poor girls may have actually been close to the top 10%, although a gigantic distance from the top 1% and an unimaginable distance from the top 0.1%
Also startup developers (proper startup developers) do not work 7 hrs, they work 14hrs.
http://www.nber.org/chapters/c2500.pdf page 101 suggests seamstress was making about 1/3 what a carpenters made. Thus seamstresses where far from the to 10%.
The US numbers look for top 10% was ~1/3 of all income top 5% = 20% of all income so 90-95% was ~10% of all incomes. The bottom 40% was 13.6% of all income. Page 32: http://eml.berkeley.edu/~webfac/cromer/e211_f12/LindertWilli...
So, someone at 90.001 percentile was making about 8x what someone at 20.001 percentile.
PS: Inflation is hard to calculate for this time-span but it was the equivalent of something like 2$ per hour.