The very same thing happens with people moving country.
Having moved from the UK to the US, I lost access to everything I'd purchased when I updated my billing details (no longer having a working UK credit card).
All Apple support could do was give me a list of the software/music I was missing, I presume to make re-purchasing easier.
That's so bad. Account management has always been abyssimal.
No account merging, no transfer of purchase is a part of it. I found the easiest way has always been to keep multiple accounts and switch accounts when switching stores.
But when I say "easiest" it's more like "less horrible than all the other way you can get screwed" and you still have to so many battles to fight to have your content where you want.
Having moved from the UK to the US, I lost access to everything I'd purchased when I updated my billing details (no longer having a working UK credit card).
All Apple support could do was give me a list of the software/music I was missing, I presume to make re-purchasing easier.