I read that running Ubuntu through a virtual machine such as VMware Player or VirtualBox is actually less costly on a laptop's battery than Wubi because it utilizes Windows' drivers, which are optimized for Windows by the hardware manufacturers, as opposed to the Linux drivers, which are less optimized and thus more costly for your system. Is this true for Wubi? If so, is it also true for a "normal" Live CD/USB installation?
This is not universally true. Some manufacturers/brands of laptops, such as Lenovo Thinkpads, give about equal battery life in Windows or Ubuntu (from personal experience).
Note that everything which applies to a regular/dual-boot install also applies to Wubi. Wubi is only slightly slower/more CPU intensive than a regular install because it stores its filesystem on the Windows partition (NTFS), and therefore I/O has slightly more overhead associated with it.
While a virtual machine may at best be only 90-95% as efficient as a real machine, if your laptop has problems like the above, then yes, virtualization in Windows with the "working" drivers/power management will most probably use less battery than running Wubi/Ubuntu.
Sadly, there's no way to tell how compatible your laptop is until you try it -- spending time tweaking it, use it for a while, ask a few AU questions, etc. to see if you can get great battery life (or not). The laptops that do work well with Linux (Thinkpads, etc.) are usually sold as "business/corporate" machines, and have a price premium associated with them. It's fair though, because I suppose this premium partly enables the use of higher-quality/better-supported internal components.