Directional pricing, on the other hand, is the norm, not the exception.
And so it should be, as they are rendering a different service to a completely different market, which may be prepared to pay much more or less, depending on local economic conditions, not to mention +/- x% for currency differences.
Exactly the same is true for UK rail fares - I have been charged a couple of £ more for London-Coventry RTN as opposed to Coventry-London RTN, even when in this case, the legs (off-peak) could be taken in the same time slot. As for peak demand into London in the morning, it is much greater than in the other direction - walk up fares don't always reflect that, but advance fares should.
And there have been cases of people with advance tickets alighting, e.g. in Exeter when they are ticketed to Penzance (from London), and being levied a £150 surcharge for breach of contract.
I think the concept of passengers breaching contract sounds so odd when operators fail to deliver the service as specified so often (delays, canx, re-routing, lost bags etc) - but a lot of the time the contract exempts them anyway.
Low cost airlines also seem to get away with a few subtle differences too in different directions, but I think a lot of this is down to currency calculations - Ryanair famously working on 1:1 parity £ to € for a while (when it suited them of course).
Were LCCs to make significant inroads into the long haul market, maybe this pricing anomalies would start to get ironed out, but I think we know the economies of doing so are stacked against them.