Why is the data storage industry locked in by hardware?

Why is the data storage industry locked in by hardware?

"And the potential separation of storage hardware and software is not restricted to the use of open source OSes. Vendors such as LeftHand and DataCore, for example, already offer their SAN products as software, while the likes of Nasuni and TwinStrata sell virtual NAS devices that only exist as software too. Logic seems to suggest that one day it will be common for customers in businesses of all sizes to buy storage operating systems, processing power and disk hardware separately. But when that day will come is open to speculation. "