A company like blizzard with so many brains behind.

Here's my take.

They know there are bots.
They still made goldskin.

Hence

Botters benefit them somehow.

After all.. we don't hear of botters getting banned much.

Botters devalue gold. In time, you'll need more gold to buy mediocre items. You cannot farm that much gold manually. Eventually, you will find the requirement to trade, and buy gold.

Transactions = money i guess.

Some way, somehow, one would be tempted to use RMAH.