You don't understand. If the cell is only serving you, your figures are correct. In real usage, and more so if everybody tries to use voip, umts (or hsdpa, which really is umts with a better modem) degrades. You won't get that upload. What is so difficult to understand? Radio is simple: you have one medium and it has a maximum capacity. Whatever tricks you use, when the capacity is exhausted, that's it.
You don't have that problem with wires, because it is not a shared medium. When some users bog down their connection running p2p clients like mad or having skype relaying the traffic of half the planet, it is not a problem for the rest of the users. You have a problem with data over air, because when one user abuses the cell, everybody's connection goes dripping. And building additional cells costs money.