Earlier quoted context omitted.
There's a solid technical reason for that though, as ISPs have no control over the performance of your connection's remote part. Sure, it leaves plenty of room for abuse, but this is a necessary disclaimer, not some slippery marketing.
Does anyone in the US actually get the “up to” even plugging directly into the ISP provided modem at off peak times?
When I was on ATT gigabit fiber in San Jose, it was hard to confirm the speeds, but they would vary a lot more. I think most of the time at peak I would only see 400 Mbps down, but closer to the line speed off-peak. Upstream was more consistent.