I moved country, changed iTunes stores and now my Apps can't be updated!?

Hi,

I know about how to change country etc for purchases in iTunes, this isn't about that.

I had a UK iTunes account and bought apps there.
I've now moved to Australia and changed my iTunes account to Australia using an Australian credit card, and I've bought some apps here.

iTunes is telling me that I have a bunch of Apps I can update, though when I go to update them it says there's none available.

I've gone to the UK iTunes Store and clicked update, and there they are - but they won't download as I need to change my billing info again.

So, here's the question - is iTunes actually that limited that one account can only have one credit card linked to it?

I live permanently in Australia now, but have purchased over 100 Apps while in the UK... am I right in saying that every time I want to update an app I have to fill out all my UK credit card and billing information, update, then fill in all my Australian billing details again when I want to switch back to the Australian store... over and over again for the rest of my life!?

I understand some Apps won't be available in one country VS the other, that's not the problem here. This is with worldwide available apps - I can see the apps in the Australian store, but because I've bought them in UK I can't update them in Australia.