With all the buzz around Compellent's announcement of new server-based controllers and a new version of its software, one of the company's most customer-friendly business policies got short shrift. Owners of older Compellent systems can run the new software. If their systems are new enough to have PCIe slots, users can add the FCoE and SAS connections, too.
If you buy a Compellent system and license features, such as Live Volume, those licenses belong to the conceptual system on which you install them. Replace the old controllers with new Nehalem-based controllers and it's still the same system and the licenses go with it.
Compare this with the traditional custom hardware-based system. At some point, new versions of the array software won't run on the old system and you have to swap out at least the controllers, and possibly the drives and drive trays, creating an all-new system. If you want features from the old system, such as snapshots and thin provisioning, on the new one you have to license them all over again.
If a Compellent system stays in your data center for 10 to 12 years, with hardware and software periodically replaced, you could save a bundle on feature licenses alone, compared with how they could add up over the two or three upgrades that a system from a more conventional vendor would need over that same stretch of time.