From what I've seen, certainly in the UK, product line-ups are being altered because some router manufacturers have withdrawn the WPS feature. Most notably the BT Home Hub no longer has WPS and the feature has been disabled with firmware updates on older versions of the hub. As BT is probably the most popular broadband provider in the UK, its decision to abandon WPS carries a lot of weight here.
In my experience, I have no idea why, but WPS rarely worked even when it was considered to be OK to use.
I understand that WPS is vulnerable due to some major flaws. My question was more about the exchange of data between the AP and the client after the button is pushed or the PIN is entered. I couldn't find anything on the details of the protocol used for that exchange. If the vulnerable PIN method was removed from the WPS standard, how secure would it be?
I don't know the specifics of its vulnerability, but even if the PIN method is removed, that requires a whole new version of the standard to be drafted, agreed to by the major manufacturers and rolled out. That takes time.