While it would be a trivial task to provide a full Windows-based installation program for BootIt NG, it is not provided for one main reason:
Although most systems will work fine, you don't know ahead of time how compatible or bug free your system firmware or hardware may be. Many people are unaware that their system could be buggy or non-PC-compliant even if it can boot and run Windows.
This is because Windows only uses the BIOS sparingly, while BootIt NG uses it extensively. Some firmware and motherboard manufacturers don't fully test all aspects of the BIOS before it's released. This means some systems may require a BIOS upgrade to work correctly with BootIt NG. In addition, other systems may require BootIt NG to use a different video mode setting than the default mode.
By using the diskette/CD boot method, you are assured that the system will boot and work correctly before installing it to the hard drive.