I have the same problem when using Fusion with my MBP. I was at the airport the other day and had about 1hr of battery when using Fusion. When I had left the house I had a fully charged battery (about 3.5 hours now).
I'm going to blame Apple on this one. MBPs use the same chipsets, processors, ram, hard drives, etc that tons of other laptops do, there's no reason why Windows should use so much more battery life compared to OSX.
I didn't RTFA so maybe they did this, but a simple test would be to take a windows laptop and a mac laptop with similar stats, load up windows 7 on them and see what happens. It should be similar if its a windows problem. And it isn't even a race at this point, if the windows laptop gets something like 4 hours 10 mintues and the mac gets 4 hours 30 minutes, then they're still similar. If the windows laptop gets 4 hours 10 minutes and the mac gets 2 hours, something is up.