Or, alternatively, they're using a large hardware RAID array which makes an SSD a pointless expense.
Afaik you would need something like a 6+ disk RAID1 array to match the random access times of a good SSD. Talk about a pointless expense
The SSD is probably the less expensive option if all you care about is boot/load times. (again, afaik)
Oh, and linux software raid ftw!
I know people with 6+ disk RAID5 arrays. Hardware with battery backing and RAM for performance. They make SSDs look like cheap toys, oh, and they store terabytes, not gigabytes.
And yeah, software RAID is great.. Except it doesn't scale all that effectively to large arrays. A hardware controller is a much more effective option for arrays containing more than a handful of drives.