Ubuntu can not be installed on a Windows VHD
From Microsoft Technet we can see the following note for a bootable Windows7 virtual hard drive (VHD):
"Bootable VHDs are VHDs that contain a Windows image."
This means that these drives are technically not meant to be able to boot any other OS, and they will be formatted with a Windows compatible format which is not the format Ubuntu needs for booting and running.
Someone may find a hack on how to boot to such a drive. But because Ubuntu provides a similar technology with booting from a virtual drive on Windows (see Wubi Ubuntu Wiki) there is not really a need for such a hack.
With Wubi, as with Microsoft VHD we do need to at least change the default bootloader in order to have an OS selection on boot. If you do not like this either you may want to consider installing Ubuntu in a virtual machine, but this will lead to a performance drop as compared to a real installation.