"it's just been assumed that the data can be treated as interval data"
Which is especially problematic since user generated ratings are ordinal, not interval data. Since the idea of an interval between points in ordinal data is essentially meaningless the summary statistics you mentioned are not meaningful either.
It's one thing for Amazon to come up with a mean user rating to give you a sense of how people like something, but it's not a valid method of comparing the data we have here, especially when the differences are so small
Which is especially problematic since user generated ratings are ordinal, not interval data. Since the idea of an interval between points in ordinal data is essentially meaningless the summary statistics you mentioned are not meaningful either.
It's one thing for Amazon to come up with a mean user rating to give you a sense of how people like something, but it's not a valid method of comparing the data we have here, especially when the differences are so small