My charger never goes to 4.2 volts either. But .03 to .05, even .15 (or even a bit more) variation is nothing to be worried about and something you'd never notice if you weren't checking the display readout. And considering the wiring and connections inside a mod, I doubt it's possible to ever get two of them with exactly the same readings. At least for the 30 or 40 I've owned, I've seldom seen it. Boards are not designed to give precise, 99% accurate lab quality readings. If they were, none of us would be able to afford a mod.
As for the charger slowing down as the battery gets more full, that's what a good charger is designed to do. At a level close to the shut off point, the charger is essentially trickle charging by design. Sort of a bad analogy, but you don't approach a stop sign at 50 mph and then slam on your brakes 10 feet away from it.
So yes, it might stop charging a bit below the maximum voltage level. But IMO, it is absolutely nothing to be concerned with.
I am seeing some interesting behavior on the new MiBoxer charger I recently bought. It has a number of amperage levels and chooses a specific one for each slot depending on the internal resistance of the battery you've installed. I haven't actually tracked it, but after maybe 15 or 20 charges it seems like it's becoming clear that I can immediately tell my older batteries without checking the dates. Their internal resistance seems to be higher as the charger selects a lower charging rate for them.
I'm hoping that I'm not just imagining it so that I now have a concrete method of deciding when it's time to give up on a cell and recycle it. No more "Hey, is this thing not lasting as long as it used to?"