it's a different architecture...
As far as I'm aware SIS was gone in 2007 apart from for attachments anyway. There's no such thing as exchange 2005 as other posters have commented.
SCC (Single copy clusters) have gone in 2010 replaced with DAG's (Database availability group) which is the evolution of 2007 CCR (Cluster continuous replication). This means realistically you are going to go for 3 copies of a database.
Now you could put those copies on expensive SAN, but the since the IOPS requirements of exchange 2010 is much less you can use SATA disks in DAS. HUGE cost savings here despite needing 3 copies of a database. Now for the SATA disks your looking at 1 or 2 TB of storage available per disk, each disk has a set amount of IOPS available and each user has an IOPS requirement based on their mail profile (sent / recieved / size). Mail just sitting in their mailbox doesn't really put additional load on the server.
So you end up with a user count per disk. let's say that's somewhere in the 100-200 user region, and you plan 1 DB per disk. The DB can then grow to 1TB or so, (not the 100GB reccomendation in 2003) and the extra space users are getting (25GB mailbox anyone?) is basically for free as there's no IOPS requirement for data just sitting there.
The 1TB example above assumes no RAID, but with 3 copies of a DB you effectively have RAID database managed at the exchange server level not the disk level. Much more flexible :)
The requirements for 2010, disk wise are therefore SIGNIFICANTLY less than for 2007 or 2003, to the extent it's got storage vendors shaking in their boots because they're not going to be selling as much high end SAN with big arrays and expensive, fast disks.