Is that 1GB video file less than 10 minutes long?
If you're really that lacking in imagination, what the hell do you need 200GB/mo for? If the most bandwidth intensive thing you do is download streaming media, and you prefer your porn^W video at 1.5Mbps, you really watch more than 8 hours of video a day?
Some transfer protocols don't support reliable streaming. Streaming just doesn't make sense for the most bandwidth intensive tasks.
A modern game typically takes me more than 2 hours to download (with my ~2km ADSL connection). That'd be ready to go in 15 minutes at 100Mbps.
A 200GB cap equates to around 600kbit/month, so what your actually getting is a 600kbit connection which is burstable to 100mbit.
Now you're getting it! The original question was: "what is the point of a speed that fast with a download cap that small?". The answer is kind of obvious, right? "[The] connection [...] is burstable to 100mbit."
Not sure of the relevance of 600kbps is though - I don't know too many people that aim to spread their quota evenly throughout the month. Most downloads are bursted.