The Krita Foundation publishes separate 32-bit and 64-bit versions of Krita. In contrast, when the PortableApps Krita setup file (currently KritaPortable_4.1.3.paf.exe) is run, it installs both the 32 and 64-bit versions (the Krita and Krita64 subfolders). The problem is these subfolders are big. The sum of the two subfolders is 656MB, with each of the two subfolders taking about half that space. The entire PortableApps Krita is less than 1MB larger. PortableApps Krita is one of the largest apps published by PortableApps.com and the largest app in the Graphics & Pictures section.
The launcher for PortableApps Krita is KritaPortable.exe. It detects if the Windows version is 32 or 64-bit, and then runs the corresponding version of Krita. In my opinion, PortableApps users should have the option to install one or both versions. By installing only one version, a user would save on storage space. The application name could reflect the choice. For example, Krita Portable 64 for a 64 bit-only version.
PortableApps.com describes Krita as a “tool designed for concept artists, illustrators, matte and texture artists, and the VFX industry.” I suspect that these groups would be using 64 instead of 32-bit systems.
As an aside, according to Krita.org, the OS requirement for Krita on Windows is version 7 or higher. But the Krita page on PortableApps.com also lists Vista as an acceptable Windows version.