degree classification is not universally standardised despite what certain members persistently claim.
Look at it this way:
1) it should be quite obvious that students at the top universities are generally (of course with exceptions) better/smarter/more studious etc. than the students at the worst universities.
2) Students at the top universities work really hard. So do students at the lower universities, but they definitely do not work significantly harder (on average, again) than students at higher universities. Take a look at the Cambridge/Oxford forums to get an idea of how hard these students work.
3) If two groups of students, one more gifted than the other, work approximately equally hard (and I would even argue that the students at the better universities work harder than the students at the worse universities) then the group of more gifted students will learn more in the same time.
4) If final examinations were equally hard at all institutions, the more gifted group (which has learned more) would score significantly higher marks than the less gifted group. However, there is not a significant difference in the amount of 2.1s and 1s given at Oxbridge and at the bottom unis.
5) For the less gifted group to score approximately the same amount of high marks as the more gifted groups, the exams need to be easier.