Hi there,
I'm more sure specifically why people may receive lower offers, but there have been some rumours and a couple of reasons on the Exeter application page.
- If you have been to a particularly under-performing school, they may give you a lower offer. They actively encourage to recruit those from under-performing schools to add to the diversity of the programmes and it reflects very well on the university.
- If you have had extenuating circumstances, which have affected your grades, and have shown potential in the other aspects of your application - i.e. your personal statement and references, they may be subject to offer you the lower grades.
Applications are ultimately assessed on an individual basis. The university may think that if you have an extenuating circumstance that may be a problem at university, they may offer you the higher grade because they want to make sure that you can cope with the demands of a degree. There may even be cases where you show an outstanding application and they really want you and give you lower grades to achieve.
I have experienced this myself, as I applied for Geography (AAA-AAB) and was lucky enough to receive an AAB offer. My college was not under-performing, but I did apply with extenuating circumstances. I got the grades and have deferred my entry as I was awarded a scholarship (not from the university), so I am starting in 2015.
If you do not have extenuating circumstances or come from an under-performing school, I would ultimately expect the higher offer if you receive one - from the stalking page last year, lower offers do not seem to be given out a lot.
Hope this helps and good luck!