"Cores, Arcades and 20GB non HDMIs" for good.
It's because of their "high failure rate" and the "difficulty and cost" of repairs. They'll "continue to trade" but they'll be submitted as a "regular faulty return" and trashed.
A spokesperson for GAME said it was simply because customers don't want the older machines as people turned their focus to the new shinier SKUs. However an internal Gamestation memo reveals a little more behind the decision.
"As of Saturday 3rd September we will not be selling Pre-owned Xbox 360 Cores, Arcades and 20GB non HDMIs. This is due to the high failure rate of the console and the difficulty and cost of repairing them."
"We will continue to trade these consoles in but they will need to be sent back to the DC as a regular faulty return where they will exit the business."
The initial waves of Xbox 360 machines suffered the now infamous Red Ring of Death where Microsoft was faced with a high number of faulty machines they had to replace. It eventually lead to the platform holder extending warranties by three years.