Madrid's metro has always been my favorite. Very extensive network, high density of stations, inexpensive (1€ per ride last time I was there), and most stations are pretty modern.
Then you're using a different definition. In this context, self-sufficiency refers to its financial and organizational position within the United States government as an agency to manage its own finances externally from the Congressional Budget Office and has nothing to do with its bottom line. The USPS is currently running a deficit but has also ran a surplus:
"Despite record gross revenue of $60.1 billion, the U.S. Postal Service ended fiscal 1998 on Sept. 30 with a $600 million profit, $100 million more than projected, but leading industry officials were hoping the USPS could at least match, if not better fiscal 1997's $1.2 billion surplus, which was less than the $1.6 billion recorded in 1996 and significantly lower than the $1.8 billion achieved in 1995."
http://directmag.com/news/marketing_observers_fear_end/
Corporations borrow money, especially when they run a deficit. Yet unless they're a larger part of some organization or the government, most people would call them self-sufficient--the ability to manage their own financial resources.
Sure the most strict definition of "self-sufficient" is to have absolutely no reliance on any external entity for anything, but by that definition then not a single organization in this country is self-sufficient.
The US Postal Service gets virtually no subsidies and is a self-sufficient organization. It borrows money, however.
"Since its reorganization into an independent organization, the USPS has become self-sufficient and has not directly received taxpayer-dollars since the early 1980s with the minor exception of subsidies for costs associated with the disabled and overseas voters. However it is currently borrowing money from the U.S. Treasury to pay its deficits."
I have always thought that there is a reason (or can be, depending). When the capital city is also the largest city, the rest of the state can often be ignored (a complaint from many about Boston, for example). If the capital is outside of the major cities then the government can better focus on the state as a whole without getting involved in local politics (think Albany vs New York City).
Also, often capitals are moved outside of major cities due to population and infrastructure, as sometimes larger cities can't sustain any more growth (which is what happened to Malaysia).
San Francisco has interestingly never been a contender for the capital, as before Sacramento it was Monterey (and Benicia and Vallejo but those were just stints). And if it were, the odds of the State focusing on the Bay Area before anywhere else could indeed become an issue.