When a provider needs to decide on it's next 100,000 "free" routers to provide to new customers, it shouldn't come to anyone's surprise when "cost-effectiveness" turns out to be its first priority. So I'm all for removing as much functionality as possible from any ISP-provider CPE; no wireless, just simple bridging.
But I really must respectfully disagree when it comes to separating out the wireless from the NAT box.
From a security point of view, having two manufacturers and two devices where one would suffice increases the attack surface -- it increases the likelihood that you have a security-related bug somewhere.
It increases the management burden -- now you have twice the number of devices whose firmware you have to keep up to date (if you're security conscience).
It doesn't scale well if you want more than one extra guest SSID or VLAN - sure you could attach a USB hub and half a dozen usb nics, or buy a VLAN-capable smart switch, but do you really want 3 Wi-Fi boxes, 3 unmanaged switches, and one router when just one Wi-Fi router would have worked fine?
There are definitely some advantages to separate wireless boxes. You can run guest SSIDs on different frequencies than your trusted SSID for example for better spectral efficiency. There are also cases where it's more convenient to have a NAT box near the CPE, and a separate Wi-Fi box centrally located. However in the average home setting, a single Wi-Fi/NAT box from a manufacturer with a decent track record is more practical.