Although people may argue why this and that person was not on the Wall Street's quant elite list, I'd say that the authors picked an amazing list of 25 quants, representing quantitative equity portfolio management, market microstructure, derivatives pricing, and risk management. Yes, as you may not be aware of, there are two types of quants, one in quantitative equity/market microstructure and one in derivatives pricing/risk management. They are somewhat related, but use very different tools. The former is less well known until early 2000s (the boom of market neutral hedge funds) and the latter is overly covered in academic programs since late 1990s.
It's very interesting and inspiring to learn how these 25 quants became quants. Many with physics/math background came to finance, due to the cut of funding in hard science after the cold war. Many people became quants because of "accident". Few people came to this world because they had wanted to do quant finance from the beginning. Of course, it's all different now. Smart and ambitious university students aim at quant finance from day one. There are also many graduate computation finance/financial engineering/math finance programs to choose from, so you don't have to go through a lengthy PhD program.
Life is highly path dependent (as many of the 25 quants said in the book). Choose your career careful, but more importantly, choose something that you really enjoy (and hopefully, also something you are really good at) - this is one of the key messages in the book. I'd highly recommend this book to anyone with a keen interest in joining the quant finance world.