Those companies that only have the three levels (Junior, Intermediate, and Senior) are generally speaking not looking for Finders to fill their senior-level positions; their business model just doesn't call for it. At most, their looking for Solvers who can also give direction to the more junior engineers. In many places that's all you need.
However, I think at companies where technological innovation is a strategic business value, you need to be able to distinguish between different levels of Solvers (Senior vs. Staff engineer) as well as identify and reward Finders (Principal and beyond).
I think its important to have the larger list of job titles because I think it communicates valuable information to non-engineers, but I also think separating out this notion of autonomy is really useful and I think can help a lot of technical people think about where they want to go with their career. Thank you for sharing.
[0]http://changelog.ca/log/2013/08/09/software_engineer_title_l...
edit: minor grammatical issues