Turbo Boost works with the older i7 dual-core CPUs on Windows, so if it doesn't work with the quad-cores it's more likely a firmware issue than a Windows issue.
computerbase.de did a recent test on the new 2011 MacBooks as well and they also found out a heating problem that would force the CPU to reduce its speed. They state, that it even happens under normal workload and not only while gaming.
In StarCraft 2 full details the MacBook Air even comes close to the new 15" model, because of the reduced CPU speed