"For now, it remains unclear as to what has caused this transaction confirmation switch. There was no official communication from either Steam or BitPay regarding this change.It is possible the company was experimenting with some settings, although it seems a bit odd to do so.

Requiring zero confirmations for transactions is often seen as a security risk. Bitcoin double spends may occur at any given time. This is why Steam has partnered with BitPay to process cryptocurrency payments. If a double-spend were executed, the payment processor would be responsible for any financial losses.

To be more precise, BitPay would be held responsible based on which risk settings Valve has set for the Steam platform. It is good to see the platform process Bitcoin payments quicker again. We can only hope to see some statistics regarding Bitcoin usage on the Steam platform in the future."

Yes, i have exactly the same opinion here, otherwise in case of a double spend or any other cause that lead to reject the transaction then i think steam will interfere in some point to oblige the user to resend the payment..

Then bitpay has to be careful and for sure it will filter the incoming transactions as you said and divide it by their probability to confirm. I think it is still a risky adventure from their side