There are 3 issues here.
The first issue is that discovery only require 5% of the outstanding balance to be repaid, so under NCA all they need to determine is that you have enough disposable income to settle that 5% each month.
This highlights the second issue, and probably the main reason for the high limits. Credit cards can be used for Transactional Spending. When I got my discovery credit card, half my transactions that I used to pay via EFT or Debit card, I started putting through my discovery credit card. Why? Well, I get cash back discounts, discovery miles and 55 days free interest - which basically means I am saving my salary for a whole month before I settle the outstanding balance in the card. If I had a lower limit, I wouldn't be doing all the transacting. I probably hit my limit every month and settle about 99% of it on payment date.
The final issue is the actual limit. I am more comfortable having the higher limit. As an adult, I am perfectly capable of knowing what I can afford to spend and what I can't. Just because Discovery gave me a high limit, it certainly does not mean you have to go out and spend it? As for being worried about your card being stolen, there is fraud and lost card protection on all Visa's so that's a non-issue. I prefer to have extra-facility available to help me through a bad month if I need it or if there are large unexpected expenses that I CAN'T AVOID. Also, as mentioned, most of my credit card transactions are what I would have spend already - so the higher limit enables me to put everything through my card (while earning interest on my cash).
Most people see credit cards as bad, and you shouldn't have debt. I prefer them. I get rewards, the retailers pay the transaction fees, 25-55 days interest free and convinience. What's not to love?
I hardly spend cash these days and all my transactional spending happens on my 3 credit cards while my full salary sits in my cash management account earning interest while I enjoy the interest free period of the credit card. I am maximizing the benefits.
Each to their own I guess. One thing I can bet is Discovery would have been happy to fax you a new quote with a lower limit if requested. Rather let them offer me the highest limit they are willing too, and if I don't want to spend it all, or want it reduced - it's my choice. Otherwise next week there will be a thread, OMF discovery only gave me a R2000 limit. WFT can I buy with that.