Me too
I actually flush the brake fluid atleast twice a year. I ride about 20,000 miles a year and we have huge temperature swings, so condensation could be an issue.
I find there is always moisture, sometimes alot of it on top of the rubber diaphram in the master cylinder, plus the color change of the fluid to me means flush it.
I find that when I do tire changes I quickly run a q-tip or 10 around the brake pistons that are out and exposed, then pump them out slightly to clean the rest, push them all the way in and then pump them up once the wheel is back on and they are rock hard once again and I didn't force and road grime or brake dust past the dust seal into the fluid seal.... I have seen several (especially 6 piston calipers) that have water actually standing under the very bottom piston that is very hard to get out once there, I have tried turning them upside down and only working that bottom inside or bottom outside at a time to force it back near the bleeder, and with a complete seal kit running nearly $180 for my bike, I don't really relish having to take it apart and replace all those if I don't have to, far easier and less expensive to spend 10 minutes each tire change and clean them up and then flush them a few times a year for perhaps $6 of brake fluid for the entire year...
The service manual doesn't say anything about flushing the fork oil but I do that yearly as well, and there is always the thick crud stuff in the bottom of the fork. Since the springs physically rub on the fork inner there is a constant barrage of metal getting added to the oil, plus the bugs that get on the fork tube inner, well no doubt some of that crap gets past the dust seals and oil seal....the valves and seals can't like this at all... So I try to keep them clean(er)