It also gives head lettuce at best two weeks at five degrees centigrade. So, two weeks at 10 degrees seems a good result.
On the other hand, the article says _about_ two weeks; they might mean 'ten days plus', and 'freshness' may be highly subjective (I bet there is a standard for measuring lettuce freshness)
Frankly, if you're not using a head of lettuce in 2 weeks something is wrong with your eating and/or buying decision making :-)