Upgraded an Escalade to Prius

I had an interesting conversation with a casual friend at a party yesterday. She said she just bought an '08 Prius, but traded in a Cadillac Escalade! I was impressed! She went on to say that her husband was so impressed with the Prius that he wants one too. They traded the Caddy because she put a lot of miles on her vehicle (+80 a day, not every day). What was really surprising was that they paid $60K for the Caddy, and traded it for $20K! I checked KBB and a new Escalade runs for $60K, but I'm sure I could get a great deal. More importantly, the trade in on an '05 with 60K miles was $17K!!! I'm not one to go for the big mama-jammas, but do they really loose their value so quickly?! She said hers was fully loaded which explains the extra bump but a 70% loss in a few short years seems extreme. I expected the big trucks and SUVs to loose their value when the price of oil went up but did it already happen or am I missing something?