I think the BE chip line is proof that AMD is giving us consumer level benefits from the knowledge gained through the OC community. When a stock 3ghz CPU can be OC'd with stability by 400-600mhz without a voltage increase, it is obvious that they are allowing us some headroom above what consumers consider reasonable performance at stock.
The problem with OEM extreme cooling, is the adverse effect that the failure of the cooling system would have. When you have a CPU fan fail on a stock Heatsink, or a poorly seated HSF with stock clocks, the computer will react with performance declines, shutdowns, warnings etc. It can normally be fixed easily, without lasting damage to your PC.
The same cannot be said about a daily OC of say, 5-6ghz running on an OEM grade extreme cooling solution. Too much liability, not a large enough of a market.