Yes, the signal to the actuators in a FBW system is analogue, but I don't see how converting to digital would improve things. If you did that, you'd need a separate computer for each actuator to decode the signal and turn it back into an analogue voltage. So now you've gone from two or three computers to dozens which increases cost and weight, introduces lag times, and provides more points for something to fail. To me, it makes much more sense just to run some wires back to the main computers.
Wow, I can't believe I'm only in my early 30's and I'm about to have a "kids these days" comment, but here it goes: I think that over the last few years, there's been a dangerous trend toward looking for a digital solution to every problem. Computers are great, but when it comes to interacting with the physical world, Newton still rules the roost (at least on the scales we're talking about here).