When there's limited resources available and you can't do everything, then sometimes difficult decisions need to be made. I personally think that focusing on the 5xxx/6xxx series was the right decision.
That's perfectly understandable, and I agree with you.
They had to choose one GPU series, and it would be unrealistic to expect Amiga dealers to scrounge around on ebay for supported cards to deliver to their customers.
The discussion was about providing support for the existing userbase with Radeon HD 4000 cards, and not about dealers offering HD 4000 cards.