Undergraduate and Masters degrees in the UK before PhD. Why do they last so little time?

I am quite baffled by the undergraduate studies in the UK as well with their graduate studies. In Argentina (where I am from) and in other countries like Spain and Greece (as well as in Equador for example), the undergraduate education lasts between 4 and 6 years. In Argentina doing a BA degree in Physics takes 6 years, in Spain it was until last year 5 years and now 4 and in Greece 4 or 5 years depending on the university. Then, in order to do a PhD you need to study another 2 (for 4 year degrees) years or another 1 year (for 5 or 6 year undergrad degree).

If you sum up you end up having between 5-7 years of pre-PhD education. In other countries e.g. in Germany, Italy, Holland, France you study a 3 year undergrad degree and then a 2 year Master's degree before you begin a PhD. Therefore in the whole continental Europe a pre-PhD education requires between 5 and 7 years of education. The PhD then lasts around 3-4 years usually.

Now in the UK a Bachelor degree lasts 3 years (i.e. like in Italy or Germany or France) but the Master's is only one year long. Additionally if you get a good mark in your Bachelor you may enter to a PhD program directly without any Masters. Thus in UK you begin a PhD with a minimum of 3-4 years of pre-PhD education. Then a PhD never lasts more than 3 years (most typically).

So, my question is how do we explain these differences? Why would a university look at a UK PhD graduate on the same standards as an Argentinian one? I am asking this because in my group in my university in Argentina we welcomed a UK postdoc this year. He started studying physics the same year as I did. Despite that he now has a PhD after 7 years of studies and I am just beginning my PhD. In our conversations I am amazed sometimes by the fact that this person has been awarded the title of Doctor by a rather prestigious university since he seems to lack very basics of my area of research.

To summarize we have the following facts: PhD time per country is UK ~ 6-7, USA ~ 8-10, Germany ~ 8-9, Argentina ~ 9-10, Spain ~ 8-10, Italy ~ 8-9, Greece ~ 9-10, Holland ~ 8-9, and so on. How do we explain (or they explain) this difference between the UK (England and Wales basically) and the rest of the world?