I believe a lot of that stuff is just additives, that do nothing for scent. Probably stuff to keep the oil from separating, preservatives, etc. Some may use extractives though, but I don't think they're lost, if you just want to smell nice. What really matters is the quality of oils, and good stuff is far from cheap. It only takes a few drops of each to scent a bottle though, so it would probably be worth it.
When they talk about perfume oil, that's the recipe of oils they use. You're paying for their recipe, and a fancy bottle. Different types have more of the oil, as this states.
Eau de Toilette or Eau de Parfum? The difference lies in the volume of perfume oil. While Eau de Toilette contains 5-9%, Eau de Parfum contains more, usually 8-14%. Eau de Parfums therefore last longer, and smell more intense.