This comment makes it sound to me like you never used PCs before the mid-90s. Before PnP, you had to set jumpers on your ISA/EISA cards. Then you had to manually configure all the I/O base addresses, IRQs, DMA channels, etc. for the hardware in your system, based on what each device was capable of using, and you had to make sure devices didn't conflict with each other.
So no, PnP is not a marketing buzzword at all. It was a completely new way of setting up hardware, and having it detected and configured automatically.
Having to install drivers has nothing to do with whether or not something is PnP. All hardware needs drivers, whether they are built into the kernel, shipped with the OS, on a disc, or online. This applies to Windows as well as Linux.