Speedtest is just a report of how much bandwidth you have, max theoretical download speed, not necessarily the practical throughput, which is what you want. Consider this:
The computer on the other end typically does not have an upload speed that matches your download speed.
You can only pull as fast as the other person can push. Also, there are many factors at work that dictate your true internet speed. Accessing an arbitrary speed server for purposes of verifying speed is different from accessing Willy's Weary Websites (3x times fast) hosted in someone's basement (worst case example), you're going to notice a difference in webspeed pertaining to
1)Your bandwidth speed
2)The other person's bandwidth speed
3)Everything in the middle
Yes, ISP companies beef up their advertisements for the sake of sales. This info doesn't get bigger sales.