By the time AutoCAD 2010 was a few years old, 64-bit systems were standard. Having a portable version that could actually utilize more than 4GB of RAM meant that "portable" didn't have to mean "underpowered."
The search query specifically specifies "64 bit." This distinction is vital. A 32-bit application can only utilize approximately 2GB to 4GB of RAM. In the world of CAD, where a single drawing file with heavy hatching or 3D meshes can easily exceed this limit, 32-bit software is a crash risk. autocad 2010 portable 64 bit