Other than anything else, the number of modules is completely irrelevant. Everybody does the same number of credits a year, they're just split differently. I'm doing 9 modules this year (8 which are worth 10 credits, and 1 which is worth 40 credits). My flatmate - same uni, different subject - is doing 12 modules this year, each 10 credits.
I would be surprised if it's true that top 30 unis do more modules than other unis, but even if it is true, that doesn't mean that they're doing any more credits. It just means that the work is being divided into smaller chunks at top 30s.