E2K10 Database size is calculated the total different way as E2K3, and a few extra factors need to be considered.
Why Is My Exchange 2010 Mailbox Database Growing So Big?
Recover Deleteded Items and Mailbox Quota’s
Exchange 2010 – Database size keeps increasing – Permanently deleted items still being retained past 30 days
Holy COW! Changes to Recoverable Items versioning in Exchange 2010 SP2 RU3