My comments weren't targeted at Lexus particularly - I think the IS does hold it's value quite well (relatively).
I just meant that, except for a few special cases, you WILL lose a lot of cash when you change, more so if you sell into the trade no matter who the dealer is.
I got offered the same sort of money at other-brand dealers, and it tied in with independent valuations based on age/condition/mileage, so it was what I expected.
The IS300 is a year old, so at least somebody else has already taken the biggest hit in depreciation for me.