I'm not sure why your example of "working it out" can't apply to 3e and earlier editions where Paladins were required to be LG?
I don't see how alignment is relevant to the discussion of how 4e in particular does it. In 4e a Paladin is a "Champion of an Ethos, an ideal", being LG has nothing to do with it - unless the paladin is espousing the LG ethos.
A god of nature might be more neutral (unaligned) and as such might espouse an ethos of "live and let live" (more chaotic), or one that is more militaristic and espouse "ecoterrorism" (more neutral evil). How does the restriction of being LG in anyway espouse those? In earlier editions the Paladin would not be able to espouse that live and let live ethos, in 4e they can. In 4e base rules the PCs would not be evil so the latter ethos would probably not apply. But if a DM and player wanted to do that they could probably work it out.
In earlier editions that was not possible at all, because in earlier editions the Paladin was only a "holy warrior for
good". Therefore, other alignments did not have champions. In 4e a Paladin is a "Champion of Ideals" - good, bad, or ugly. If you want to have a Paladin that is more tied to the virtues you can play a Cavalier, if you want to have a "fallen" Paladin you play a Blackguard. And each of those have mechanical support that works well with their particular thematic (story) elements.
Alignment is an entirely different ball of wax altogether, and one that I'd rather not get into as part of this discussion. IMO, at the game level, the "ethics" of alignment are entirely based on opinion and usually the game designer's opinions. If they were not, there would not have been as many pixels killed in the apologetics of them.
In earlier editions, the default "rule" was punish "ethical" slips. But according to the "ethics" of whom; the DM, the player, the game designer? In 4e the default is we don't provide you rules for dealing with "ethical" slips, that is entirely a roleplay opportunity for the players at the table, and DM to explore. The class writeup gives the basis of the class. The default gods have some broad generalities to them if the DM wants to hang an "ethos" on them. I would have liked some examples, but the lack of examples doesn't "break" what is there.