Re: Virtualbox with Windows 7
VMs are for convenience and running desktop applications, or testing, etc. They aren't for gaming. At least, they aren't for games that we'd classify above trivial.
The Guest Additions are needed because the VM software has its own emulated hardware platform, as well as to facilitate things like Host-to-Guest Drag and Drop/Copy and Paste, etc. That is why even the 2D accelleration is bad, and you get limited resolutions in the guest without the Guest Addidions. It's like running Windows without a Graphics Driver installed, and using the generic VESA driver.
They aren't made to replace dual boot/separate machines in all scenarios/use cases.