It's happened to me, it can happens to someone else
Right now it happened JUST to you. If and when someone else would report the same problem, perhaps we might start taking it into consideration.
But since I receive something like 10 emails EACH DAY, by users asking how to retrieve their lost purchase receipts, when this information is clearly indicated on the FAQ page, the installation guide, and a sticky post on the forum in this very section, I doubt it make any difference.
If we changed the question into a sim selection screen, some users might assume that, since they saw BOTH P3D and the FSX pictured, the installation would go in BOTH sims by default, and they simply clicked at random without thinking.
To quote one of my favorite sci-fi authors, Robert Heinlein:
"
It is impossible to make anything foolproof because fools are so ingenious"