I think the non-applicable to code observation is very likely true – we'd like to be able to write nice descriptive variable names. In doing this, we probably want them to be more than the 1 or 2 characters that Haskellers traditionally use, maybe of the order of 5-10.
Given this, it would seem a shame to only be able to fit 6-13 litterals on a line, that sounds like we'll quickly be having to wrap lines with deffinititions of any significance on them.
I really like the 80-columns rule. And I also agree that long identifiers can be useful. All this means is that you use up more lines. Note that this can be a good thing: indentation is information, so by using more lines, you give more indentation information.
My personal preference with Haskell is to ignore the 78 character "limit", but only when layout otherwise becomes horrible otherwise.
I consider screen real-estate a very valuable resource (and I'm appaled by the fact that current 21" displays are limited to 1600x1200 when they could go up to 1800x1400 ten years ago), and in this light the 80 columns limit tends to work fairly well: using significantly less (like 50) makes the code really difficult to write, whereas using more tends to waste a lot of space because, while some lines will make good use of the extra columns, most of them won't. Finally, I find that the indentation-pressure imposed by the 80-columns limit forces me to write better code: when code indentation grows too high, I'm forced to move it to a separate function, making the code more readable at the same time (by being forced to choose a name for the function and to choose appropriate arguments and return values). Stefan