If a character readies an action to move in a way that would really provide protection from a charge (e.g. moves out of charge range, moves back through a line of allies), then that should work. But I find it lame if the target can ready an action to move from one easily-chargeable location to a different easily-chargeable location, and somehow that makes the charge fail.I prefer ruling in favor of the Readying PC, not the Charging PC.
The Readying PC gave up a Standard Action for a chance to invalidate the Charging PC. The concept of "Sorry, I'm going to make your Readied action worthless" is lame. IMO.
Readied actions are famous (admittedly, not just from 4e) as a way to abuse the rules, and if an interpretation makes them weaker, that's fine with me.
You talk about a PC giving up a standard action to invalidate a charge (another standard action). That seems reasonable. But what if the PC readied an action to counter-charge the enemy instead of stepping out of the way? By your interpretation, the PC gets his attack and denies an attack to the enemy. Now the readied action has been used to generate action advantage, and that's the kind of thing that readied actions shouldn't generally be capable of, IMO.
None of that affects RAW, but I can see how it would lead us to different interpretations when the rules are ambiguous.