Fascinating thread.
In my field, relatively senior jobs are all over 100k (allow me to stay vague, cannot be bothered to namechange). To get to them you need good level experience within the field gained at a place that is well-known for your specialism and to get that experience you need to have trained (and stayed on) at a magic circle (law) firm or one of the big four. In turn, to have trained there, you need good academics (not necessarily UK ones, but from a top place in the country where you studied), drive and "polish".
"Polish" is short-hand for the characteristics that mean your firm will be happy to put you in front of clients: speak and write the relevant languages correctly, have good manners, be at ease in most relevant contexts or know how to look like you are (this includes dressing right for the roles, becoming competent in the likely conversational subjects, etc), etc.
I really do not buy the argument that the above can only be acquired in UK public/private schools or their foreign equivalents: I know plenty of people who are perfect examples of why that is not true. What really does help (and is in my opinion necessary) is drive and being willing to do the research and then mould yourself accordingly.
So, for example, if you are a young non-UK woman working in an environment where most clients are English public school men in their 50s, it helps if you can speak and write English correctly (most foreigners are taught either RP or an American accent anyway), understand English social conventions and observe them, can make conversation about the most recent exhibitions/theatre shows/books and are not completely thrown by cricket references.
If you then move to an environment where the majority of colleagues are loud barrow-boy types, you need to learn additional vocab and widen what you read. Depending on the image you have built up to then and the one you want to project going forward, you might want to learn a new hobby, read an extra newspaper, etc. It is not rocket-science, it just needs some thought.
And of course, as other have said, you need to be prepared to work very long hours (especially in the beginning) and, later on, be available in a way that people in other fields may not even conceive of. When newly qualified, my contemporaries and I worked 100-hour weeks for months or years on end. Now, the longest period I go without checking my blackberry is when I sleep, and my colleagues know that my emails start around 5.30/6am most days. But I enjoy what I do and have found a work-life balance that suits my family and me. And, just like others have said above, I am able to switch off completely in between work spells: I agree with other posters it is essential to do this sort of thing successfully, long-term and happily.