Fair enough. Any sea-oriented guided missile would have to overcome this obstacle. Still, I don't think piracy going anywhere in the next century, so the opportunity for developments in cheap fire-and-forget tech will be there. And, if merchant ships do get armed (which I think is unlikely), then the demand for guidance and some form of standoff capability for the pirates' weapons/ RPGs will likely increase.I disagree. RPG's have one major advantage when it comes to sea launches. They are fire and forget. A scratchbuilld missile is most probably going to have either TV or Follow the Dot guidance, since that's the simplest and therefore cheapest type of guidance available. Now imagine trying to hold the dot on target when your skiff is rolling up and down.
It will be interesting to see if someone eventually comes up with a new form of guidance or if future developments will just be evolutions and refinements of current basic systems.
I do agree with your basic point that GPSes are available on the civilian market far more readily than advanced weapons systems. However, the fact that the pirates made the effort to get this kind of technology indicates that they are willing to upgrade, expand, and improve certain aspects of their capability.There's a big leap from bying civilian GPS's available anywhere for cheaps to buying advanced military hardware. The pirates buy GPS's for two reasons. To be able to find their way back to their mothership and to be able to find their targets. The latter is possible via an AIS receiver, build into most modern GPS's.
As you pointed out, it isn't an analog to buying advanced weapons, and I want to emphasize that that never was my point. However, it's a first step down a very, very long road that might one day see pirates or terrorist groups with guided weapons.