I (and others) have put a lot of effort into making the Linux Chrome build fast. Some examples are multiple new implementations of the build system ( http://neugierig.org/software/chromium/notes/2011/02/ninja.h... ), experimentation with the gold linker (e.g. measuring and adjusting the still off-by-default thread flags https://groups.google.com/a/chromium.org/group/chromium-dev/... ) as well as digging into bugs in it, and other underdocumented things like 'thin' ar archives.
But it's also true that people who are more of Windows wizards than I am a Linux apprentice have worked on Chrome's Windows build. If you asked me the original question, I'd say the underlying problem is that on Windows all you have is what Microsoft gives you and you can't typically do better than that. For example, migrating the Chrome build off of Visual Studio would be a large undertaking, large enough that it's rarely considered. (Another way of phrasing this is it's the IDE problem: you get all of the IDE or you get nothing.)
When addressing the poor Windows performance people first bought SSDs, something that never even occurred to me ("your system has enough RAM that the kernel cache of the file system should be in memory anyway!"). But for whatever reason on the Linux side some Googlers saw it fit to rewrite the Linux linker to make it twice as fast (this effort predated Chrome), and all Linux developers now get to benefit from that. Perhaps the difference is that when people write awesome tools for Windows or Mac they try to sell them rather than give them away.
Including new versions of Visual Studio, for that matter. I know that Chrome (and Firefox) use older versions of the Visual Studio suite (for technical reasons I don't quite understand, though I know people on the Chrome side have talked with Microsoft about the problems we've had with newer versions), and perhaps newer versions are better in some of these metrics.
But with all of that said, as best as I can tell Windows really is just really slow for file system operations, which especially kills file-system-heavy operations like recursive directory listings and git, even when you turn off all the AV crap. I don't know why; every time I look deeply into Windows I get more afraid ( http://neugierig.org/software/chromium/notes/2011/08/windows... ).