Well I fully agree with you that this is the standard. But this service/app is not Reuter/Bloomberg and I and the other uses do not sit at bank’s treasury room. 
Nowadays all is about choice and people wil use it if the chouse would be availble.
If this option is implemented it could be allowed for advance users with disclaimer (of course). If the feature is on the screen can change color or have a special icon can ocur to tell the user advance option is on. Let’s call it “reciprocal value” to the industry standard.
The other comment is that - while using the industry standard the graph curve for the pair CZK EUR look like a staircase as show below. Basicaly you cannot set the following if i want to by EUR 100 for CZK 2568 for auto-exchange but you can sell that becase of industry standard.
|€0.0389|CZK 25.70694
|€0.0390|CZK 25.64102