I think few people would go for the big plan at that rate.
As for the lack of cheaper smaller plans thus far... I could be wrong but my theory on the lack of smaller plans is that bandwidth is more expensive than storage space. If you have a smaller dropbox then you're going to be swapping files in and out more or potentially the same amount as someone with a large account. So the cost to dropbox for bandwidth would be greater or at least close to the same.
I think few people would go for the big plan at that rate.
As for the lack of cheaper smaller plans thus far... I could be wrong but my theory on the lack of smaller plans is that bandwidth is more expensive than storage space. If you have a smaller dropbox then you're going to be swapping files in and out more or potentially the same amount as someone with a large account. So the cost to dropbox for bandwidth would be greater or at least close to the same.