If most of the USB 3.1 spec is just USB 3.0, and you only need to refer to the USB 3.0 parts to build your device, then why not just build your device solely according to the USB 3.0 spec, and call it a USB 3.0 device?

Compare/contrast: the 802.11 specification series. Each successive specification only lays out the unique new modes; with the expectation that devices support multiple specifications, where each specification lays out its own supported modes. So if you e.g. build a device that can only do 802.11n things, and not 802.11ac things, then you’ve built an 802.11n device. But 802.11ac peers — which are really “802.11ac + 802.11n” peers — will still be able to talk to it in 802.11n mode — but they do this according to the 802.11n spec that they also support; not according to the 802.11ac spec.

> People outside hardware developers aren’t expected to know USB 3.O vs 3.1

Why not? How else should you know whether your device can go at its full advertised speed?

> How else should you know whether your device can go at its full advertised speed?

Just say what speed it supports using which technology. SuperSpeed at X Gbps, SuperSpeed+ at Y Gbps, high speed at 480 Mbps. You can only use a speed both support.

But in this case, say that a host supports only 3.2 Gen 2(x1), and a client device supports only 3.2 Gen 1x2. Both would advertise a relatively-higher speed, but it wouldn't just be that you'd get the lower of the two speeds; rather, you'd get a speed lower than either claim. And IMHO this isn't some weird exception; standards are often like this. This is is the reason people care to know exactly which subprotocols their devices are capable of negotiating, rather than just knowing the generation of support.

But that's a lot of words and they already knew people don't say those terms. 2, 3, 3.1, are much easier to say, and there was no consumer-benefitting reason to undermine those terms.