So, it's basically just the default commitment Microsoft makes for new Windows versions, according to their Lifecycle Policy. It doesn't reflect the Windows-as-a-Service model at all, so is almost certainly not relevant to their actual plans.

The newer understanding is that Microsoft will release a new feature update every 6 months, and support each of them for 18 months. Almost certainly, this big refresh being announced soon will continue that model: All Windows 10 PCs will be eligible, support for existing releases will be for 18 months from their release, etc.