They are not saying that you will get to enjoy 2Mbps of bandwidth between your computer and your favorite website. The speed that is advertised is the speed between you and your ISP. There are dozens of variables that will control/limit your speed to "the Internet".
- Route of traffic to remote site
- Response of Remote server
- In many cases amount of users online at the same time.
You will probably never get a full 2Mbps communication between yourself and servers you request information from. The ISP is stating their upper limit when they sell bandwidth like this. No matter what technology you go with (ADLS, Broadband, Wireless) you will always be sold on the possibility of the upper limit. Good luck getting close to that.