[yareth]

Yes, that is common. Back when I used to work for an ISP, all of our main competitors have whitelisted speedtest servers to sidestep their shaping and sometimes even ran their own, just to look good on the results page. The fact that other webs instantly load might be just an implementation quirk; the QoS might get reset for a second when loading the speedtest page.

You can see what ISP traffic shaping actually does when you have a server on reliable backbone link outside of given ISP network by trying to download or upload large file to it and measuring. Bandwidth changes usually aren't too smooth and often you can see "stairs" on measurement graph as the speed drops the more data you transmit.

This shows how the whole "speed UP TO xyz mbits" marketing trick really works.