Exchange 2007 Mailbox Server Role Storage Requirements Calculator updated to v 13.0

We're finding this tool very useful.  Thank you for producing it.  I read through the documentation which explains each input and output in the calculator, and I am wondering why the Restore LUN Size / Node is sized to support "up to 7 databases and 7 transaction log sets".  Normally, we only ever need enough to support one database and transaction log set with Exchange 2003.  Is there something different which needs to be considered regarding Exchange 2007 or is this a Microsoft recommendation?  If so, can you direct me to that article which talks about it?  Thank you.