I sometimes wonder if the 2gb offer to each and every user is mostly for publicity. It is highly unlikely that they feel they need to have that much space for each user. Granted, the companies do need a large amount of space, but not as much as you would think.

I'm sure very few users actually fill up their entire mailbox since emails are quite small (depending on attachments). In addition, even though emails can be archived, some may still feel the need to delete emails they don't need.

This is somewhat similar to how dial-up internet companies had more customers than their systems could handle. They realized that just because they have that many customers, they won't all log on at the same time, thus earning more revenue from more customers than the support they could provide.