This is part of Google's Gmail "infinity +1" plan which they launched to celebrate their one-year birthday.
Storage is an important part of email, but that doesn't mean you should have to worry about it. To celebrate our one-year birthday, we're giving everyone one more gigabyte. But why stop the party there? Our plan is to continue growing your storage beyond 2GBs by giving you more space as we are able. We know that email will only become more important in people's lives, and we want Gmail to keep up with our users and their needs. From Gmail, you can expect more.Besides storage they also introduced rich text formatting for Gmail users.