Since 13.04, there is no Wubi, why was Wubi removed from the installation phase?
The reason there is no Wubi Available since 13.04 is because of the following points:
For more information regarding Wubi and future Ubuntu versions please feel free to read the following links:
Ubuntu Mailing List - Regarding Dropping Wubi
Wubi Famous Bugs - No Account Creation
Wubi Famous Bugs - Detection Problems
List of Wubi Bugs (300+ Bugs) - https://bugs.launchpad.net/wubi/+bugs
Some problems related to installing Ubuntu on a Windows 8 PC through Wubi - Installing Ubuntu on a Pre-Installed Windows 8 (64-bit) System (UEFI Supported)
Performance between LiveCD / LiveUSB and Wubi -
So with all of this in mind, the recommended way of installing Ubuntu 13.04+ and saving the user from many problems associated with the installation of Ubuntu through Wubi is to actually use the LiveCD / LiveDVD / LiveUSB images. They will give the user an overall better performance, less issues than Wubi and will save the user from headaches.