Dropbox is based on Amazon S3 which at their cheapest advertised rate costs 4x more than than what Google is offering. (although with Dropbox's usage they can probably get a volume discount)

I wonder if Dropbox have plans to start utilizing their own data center to get costs down...

I think Dropbox actually spends a fair bit more on bandwidth because of all the syncing. As far as I know Google has no desktop client (and if they do they failed to offer it to me), whereas with Dropbox it's really the way to go.

But in general yeah I agree, the margins of all these storage companies are very high. As I've said in other comments here, I think I can do it cheaper using consumer-priced hardware (let alone on a huge scale with hardware bought at near manufacturing costs).