Originally Posted by Globaliser

IME, BA is very consistent as to how the fares are described. E and T class are always described as "economy", and the "premium economy" designator is reserved for (some) W class fares.

I'm sure that there is a commercial reason behind it. I can guess at some possibilities, but that would be pure speculation on my part. However, the one thing that this is not is "inconsistent". It's far too consistent to be either that, or anything other than thought-through and totally deliberate.