Yes you are right and I noticed that, but given I wouldn't be keeping the card other than getting the sign on points it probably doesn't make too much difference. i.e the Platinum I'd be spending little more than $2k so earning 1000 QFF points v Signature where you have to spend $4k which gives 3000 points. But to compare apples with apples, if I spent $4k on both it's only 1000 points worse off.
Keeping the card ongoing however is a different story. Also the minimum credit limit doesn't bother me too much either way as I'd be only holding it for a short period.
I guess it's whether I want another 30k points for and additional $130 for the fee with a couple of lounge passes. I've got around 1 million QFF points and have lounge access, so my thinking was trying to avoid as much expenditure as possible on fees. If I had minimal QFF points I may have thought differently however.