In fairness I will say it's a step in the right direction to have have Lawful only but being Lawful Good makes you a bastion for everything that is good and just in the world and that is what makes a Paladin a Paladin.
Personally I think the problem with restrictions is that it is often hard to define them in a way that matches with the expectations, and the Paladin is the classic example.
Saying that "you must be Lawful and Good" sounds simple, but then different people have
very different expectations on what "Good" means.
Even worse, is a "Lawful" character someone who has a lawful behaviour himself or someone who pretends that the others behave lawfully? Because these are 2 different things, and maybe the class description doesn't tell you which one, but some players are going to think that their Paladin needs to be lawful in the sense that she will never break the law, lie, get drunk etc. while other players are going to think that if they don't force others into being lawful then they aren't lawful enough. It happens all the time in real life, there is lawful tolerant and lawful intolerant, but lawful intolerant will always believe that the lawful tolerant aren't nearly as lawful as they should be (and similarly there are chaotic tolerant and chaotic intolerant).
When this doesn't have mechanical consequences to the game the problem evaporates into a mere roleplaying choice. If it has mild consequences such as adjudicating you're properly roleplaying your alignment, then it causes attrition at the game table but it can be solved, e.g. by changing the alignment tag on your character sheet but keep playing the same PC. When it is a formal restriction, then there can be a big problem, because not complying with the restriction usually means someone is going to ask you to severely change how you roleplay your character, keep going but receive harsh penalties, or piss off other people at the game table.
Simple labels ("Good", "Lawful") can work fine for beginners for a while, but soon they're going to learn they need more than that. Personally my favourite way of handling this is to encourage the player to write down her own "decalogue" of do's and dont's, and then stick to it in roleplay (unless voluntarily wanting to RP a more complicated character story).
As for the printed books, they could definitely have a few "sample decalogues" for example for a traditional LG Paladin, for a more L-oriented and for a more G-oriented.
While we're at it, I think they should do the same for other classes as well, in particular having a few different druidic codes would be interesting, but the books should always emphasize that codes must be agreed upon between players and DM instead of enforcing something as universal and as dumb as "cannot wear metal".
Alignment
suggestions can still stay there, as long as it's clear that they are not absolute restrictions unless the gaming group wants them to be.
