If you've ever suffered thru watching DALLAS or WALKER on TV, then you've seen the Dallas skyline. Some of the most famous landmarks there are nothing but giant server farms. Forty, fifty floors of blades and AC units, battery backups and hard disk space.
I'm sure you've seen pix of server rooms with aisles of rack-mounted somethings.
This 4,000 unit sale is nothing, really. That's probably not even a tenth of one room on one floor. And they're probably replaces 500Gb HDDs at the same time - older units, maybe IDEs. There are still kajillions of those out there.
(This is where computer service companies can do a killing on eBay - buy pallettes of 1,000 drives each for $20 or $50, then when someone needs a mainboard from that drive model, they'll hope they've catalogued their $20 inventory properly. Charge $200 for that 'recovery' process and make a little extra money.)
I have a feeling that 4,000 unit order is toe-testing, and there are server farmers that have already proven the savings math. Now it's a matter of finding SSDs that live up to their endurance claims, and then move to the next generation anyway.
We have film-production clients with several hundred 2-3-4Tb HDDs now, and THEIR problem with the exchange is "We haven't amortized our hardware yet - we're still 12 or 15 monhts from our accountants letting us get rid of those!"