Or is it reindeer bladders all the way down?
In terms of the fraction example, is there not possibly a dimension missing? For want of a better term possibly, I tend to use "cognitive level". Whilst they all do cover the same _topic_, they are different difficulty levels.
The first is easy - level 1 - because the denominators are the same.
The second is a little trickier - level 2 - because, whilst the denominators are the different, they are both one away from unity, and thus quite easy to intuit.
The third is hard - level 4 in my semi-arbitrary scale - because you now have to actually normalise the fractions to some common denominator to properly compare them. That is a two step process, and much harder than the previous questions.
In my experience of the UK exams vs our local SA exams, the notion of cognitive level never seems to appear. I think that it helps a lot in setting a fair assessment, particularly if you want to avoid the whole "grading to a curve" idea, and recognise what students actually know.