Undergraduate and Masters degrees in the UK before PhD. Why do they last so little time?
I can only speak for my area, mathematics. In the UK, there is a very clear division between which degrees include coursework and which are strictly research. A Masters degree in math consists of approximately 10 (very intense) months of course work, and only on extremely rare occasions research. A PhD consists of 3 years of very intense research, and only very rarely coursework. This allows students to focus on one specific task and complete it faster. Here in the US, Masters and PhDs include both coursework and research. The research for the Masters degree means that it takes more time, and the coursework included in the PhD means that it takes more time.

In theory, these two systems are supposed to be equivalent, and both countries produce excellent mathematicians (we currently have two postdocs who were educated in the UK who are both quite brilliant). In practise, I would theorize that more years working on essentially the same level (an advanced grad student and a postdoc are both expected to be independent researchers) would of course give someone more knowledge. However, the PhD is supposed to be evidence that a person is a capable independent researcher, not that they are familiar with X number of the main methods in the field. As long as UK PhDs satisfy that requirement, I believe they have earned the degree.