While it might be true for Adapted RAID, it's definitely not the only way in the hardware world. I could take a 1995 era Compaq server with some old SCSI drives in an external enclosure connected to the same 1995 era raid card, and follow these steps to migrate it to my 2008 HP server:

1. Power down the 1995 server
2. Detach SCSI cable
3. Attach SCSI cable to 2008 server with 2008 RAID card
4. Power on 2008 server
5. Press an F key during boot to confirm RAID import.

Hardware raid isn't all bad, just as all software raid isn't all good. It all depends on the vendor, in this case either a particular hardware RAID vendor ensuring they support their products, or an OS like Linux ensuring it has a good software RAID subsystem.

For my personal stuff, I've gone both ways. I've had 3 generations of Linux servers as my storage boxes since 1998, and the second and third both relied on software raid to group several disks together. The 3rd box had disks added as I needed more space, and eventually was retired when the OS drive failed and I decided to replace the entire setup due to age. I then migrated to a ReadyNAS NV+ with hardware RAID, and new SATA drives instead of the old PATA drives of the linux box. The NAS has a 5 year warranty on it, and the company has several past products all using the same family of compatible hardware RAID in them, so I'm comfortable in knowing I'll be able to get at my data with it for the lifetime of the product, just as I was comfortable with my Linux software solution.

In the end, it all comes down to research before you invest in any solution, and then picking one that will meet your needs and that can be fixed if something does go wrong. Drives fail, as do other components. No matter what direction you go, you need as disaster recovery plan. And always keep in mind RAID is not a backup solution. Never trust your actual critical data to only be in one place, be it RAID, or your desktop computer, or even in the same building.