Technically it's not. Programs use the libdvdcss functionality built into VLC, but there are other alternatives (such as Fairmount) that also use libdvdcss. VLC

Technically it's not. Programs use the libdvdcss functionality built into VLC, but there are other alternatives (such as Fairmount) that also use libdvdcss. VLC is just more likely to be installed. Indeed, if you're running 64-bit Handbrake then the lack of a (stable) 64-bit version of VLC makes Fairmount a better option.