The Way I look at it is that buyer always pays for wrap, if there is pre wraped for 4 keys that means the hat is 3 keys and the wrap is 1 key. Backpack.tf goes by price of the hat itself and not the wrap included.

(4 keys - 1 key for wrap = 3 key hat)

http://backpack.tf/classifieds/search/bounty

- 4 keys pre wrapped seller

- 4 key pre wrapped seller

- 4.5 keys pre wrapped seller

- 4 keys unwrapped unsold

< 3 keys

http://www.tf2outpost.com/trade/9694800 - 2.75 keys

http://www.tf2outpost.com/trade/9708264 - 2.5 keys

http://www.tf2outpost.com/trade/9693144 - 2 keys

3 keys

http://www.tf2outpost.com/trade/9713079

http://www.tf2outpost.com/trade/9731253

http://www.tf2outpost.com/trade/9622453

http://www.tf2outpost.com/trade/9456003

Unsold for 4 keys

http://www.tf2outpost.com/trade/9730812

http://www.tf2outpost.com/trade/9702986

http://www.tf2outpost.com/trade/9408007

http://www.tf2outpost.com/trade/9441434

http://www.tf2outpost.com/trade/9449030

http://www.tf2outpost.com/trade/9636708

http://www.tf2outpost.com/trade/9620786

http://www.tf2outpost.com/trade/9554512

So from the proof you can see that people are selling for 3 keys and even less. There still are lots of 4 key sellers and a few of them have add's so 4 keys still needs to be in the range.