I think all of this authorization limits is nonsense.
Complaining about it here has no effect. You need to complain to Apple, who is the only entity who can do something about it.
What if you have more then 5 computers? What if you account all the computers in your home, plus the one in your work, and the one in your holiday house or something that will account for more then 5?
I would do two things:
1. Create another iTunes account.
2. Use that account on one of my computers, probably the one most distant from my everyday uses.
AFAIK, nothing prevents the use of the same credit card on multiple accounts.