Full disclosure: I work for a vendor providing storage solutions for Exchange.
This is a great article and interesting dialog. Our customer discussions have led us to the conclusion that they are concerned that deploying Exchange 2010 at scale does require a tremendous increase in storage capacity, primarily due to the number of isolated copies behind each server (driven by DAG) and the need to increase mailbox quotas (to satisfy user's hunger for email capacity). The over-the-top model with DAG is great from an HA perspective but does create a multiplicative effect on capacity required. We feel that this creates a unique opportunity for customers that want to keep Exchange 2010 on-premises but want a more compelling means of addressing the storage capacity required to support it, and techniques such as hybrid storage solutions, primary storage deduplication, and so on, may provide an attractive option without compromising performance or data protection posture.
If anyone is interested, I encourage you to check out what we've built for Exchange 2010 at: http://www.storsimple.com/microsoft-exchange/
Thanks,
Joel @StorSimpleInc