It's not an assumption. Here is one of many completely random videos of my car at the track, you can hear it spinning up until a little before the 330' mark (before it migrates into the typical tread noise), at which point I'm normally somewhere around 80-90mph depending on the tire setup. The reason people don't think these cars are spinning on the street is because there's no smoke and/or there's not much noise. It's not blowing the tires off at 80mph, it's just spinning a little. You can hear it at the track and not on the street is because there's rubber everywhere and it screeches when slip occurs between two hard rubber surfaces. It doesn't make much noise when the drag radials are on because they slip less and the compound is much softer than the track surface.
Cars at the dragstrip are not faster solely because they have more power. No offense meant, because not everyone is into racing, and may not understand basic things about it.
Kind of goes over into the brake discussion as well. I have datalogs on dragy showing how bad the OG OEM pads are compared to PFC pads and then CCBs on high speed stops. I don't post data because the next excuse would be something like "but the air temp was 4 degrees warmer" or " how do we know you weren't on semislicks?" etc.