Cable companys are setup vary bad.
For example. Comcast. Although you may have a 8mb/768kb service, you will never reach those speeds for one reason. Network sharing. Now you may be saying "well I don't share my network with anyone, its just me in my house." The fact is cable company's make yous share your connection with your neighbors. Sounds lame but its true. Every person on your street and in your neighborhood will all share the internet. You might be thinking "well why do they do that". It saves them money.
Look at Verizon FIOS. Its "Fiber to your home" meaning that you get your own private connection straight to your house. They are the first company to offer this kind of service. If you think I'm lying here's a great story. My uncle has Verizon Fios 10mb/2mb. I have Comcast 8mb/768kb. While downloading the same 700mb file from the same source at the same time, he downloaded said file in 5 minutes, it took me well over 45 minutes. Comcast's sharing with your neighbors is a pain in the ass and I personally am happy to say I will be getting rid of their horrible service in a few weeks. (when fios is available. The streets are setup we just need the green light.)
Then with FIOS I'll be buying the 50mb/20mb service for 139.99/m.