AMD did this for the gamers who are buying used cards off of eBay that have strapped bioses.. it's a way to adjust timing back without reflashing the stock bios...
This is one possibility however I don't think its the reason. Just a coincidence that it was added at a bear-market with GPUs being sold.
If someone sells a GPU on eBay and they don't flash back the stock bios and the buyer has issues with the GPU, they risk of getting bad feedback and having to perform a return on the GPU and risk losing money on shipping both ways.
I am pretty sure most people kept a copy of the original bios and just re-flashed it during the sale. The memory straps weren't the only adjustments made, some people adjusted the voltage, memory, core clock, etc. Hence its essential for a stock bios re-flash.