Its not just about downloading MORE. It's also about downloading faster. When i upgraded from 4Mb to 20Mb, i didn't change my download patterns, i didn't start donwloading more just because im on a faster connection. All that changed was that what i would normaly download is now downloaded faster.
So even with STM, its possible to download faster then the other tiers that are offered. And even with downloading many GB of patches, games on steam, ubuntu and such it's easy to time the downloads so you will never be hit with the STM.
Also, there are some ISPs which will simply kick you off their service, or charge extra if you download large ammounts, with VM, you can max your connection 24/7 for a whole month, and although you will get hit by the STM you wont have any extra charges or be warned about excesive usage.