It is not necessary. My gold card can go up to 15K so does my platinum. In a way, it depends on the bank but they have a cap (max. credit limit) for different cards.
Btw, I used my existing card to apply, didn't submit any pay slips

I hold a UOB Platinum and there are many other exclusive benefits compared to normal Classic/Gold (just like any other Platinum cards). Plus, you have a special hotline to call instead of the normal general number. The annual fee is waived as long as you have at least 6 transactions a year so literally, it's free The ONE Platinum is targeted for younger people and have many other privilledges as well (they gave it to me but haven't used at all till today).

siutimtim, different banks would have different benefits but HSBC Platinum is not bad. The tough part is the annual income requirements are pretty high too