To me the real issue is not what the old alignments stood for. It is not whether the new system is linear or not. it is simply - "What can we use the alignment system for?"
First of all, alignment is not at all important in character development for me. Both PCs and NPCs get their alignments as an afterthought. And, in general the label never really matters.
Still some of you might have noticed that I kind of dislike this new system.

Why?
Because alignments are useful for setting up broad conflicts within a setting. It gives me as a DM a shorthand for describing groups, tribes and monsters (not every individual of them, but general trends). In the fantasy story you tend to have a conflict between A and B, and the hero/heroes choose one of the sides, fighting for it in various ways. The standard heroic story is about good fighting evil. And that is fine. It is easy to get into, and works especially well when you don't want too much philosophy an debate in the way of the action. The weakness is that the heroes don't really have a real choice in how they are going to act.
And sometimes you want to challenge the players. You want them to make a choice where right and wrong aren't obvious. The easiest way is the dark story, where both sides are evil and your heroes have to decide which is the lesser of them, or which can easiest somehow be influenced to do good instead. This sort of story is also fine, the longest campaign I ever played was one of those, and lots of fun was had there. But this story often has the problem that the characters don't really get to feel like heroes. They feel like they are forced to work for something they don't like. Too much of that, and frustration takes over.
Any other solutions? Good vs Good? I have played one campaign in the 80s that tried that as a subtheme, but then using the LG paladin civilization vs the CG "barbarians". It is doable, but best as political conflict rather than military. "Good" doesn't really want to kill "good" after all, even if they worship the wrong gods or have unacceptable laws.
Unaligned vs Unaligned? (Unaligned vs Evil works as a less powerful subset of Good vs Evil, as does Good vs Unaligned.) Well this is probably where I will have to go with future storylines myself, if I want to stick to the official rules. This works fine, you can yourself invent why the conflict is there, and the heroes can both debate which is side is really right and actually want to defend the side that they choose to work with. The heroes will often change sides in these kinds of conflicts, or work for both sides at once. Fun stuff.
The 1.0 to 3.x solution here was usually to run Law vs Chaos, which meant that you could use lots of stuff both from MMs and various fluff descriptions to help you along. Good and evil characters could show up on both sides, which could make for very colourful storylines and battles. And what stops me from doing Law vs Chaos in 4th edition? Nothing. But on the other hand, if the rules have alignments where chaotic is a subset of evil and lawful is a subset of good, then it does seem a lot harder, doesn't it?
What I think will be the loss for my way of writing in 4Ed is the lack of creative support from the game. Races, cultures, organizations and monsters will mainly be made for the Good vs Evil mindset. I can still use their creations, but I will probably need to tweak it all, at least from a fluff point of view.
If I am the only DM who feels this way, then their choice is absolutley correct. But if there is a more significant minority who like the kind of stuff that I talked about here, then they have made a mistake. After all, the options added by a Law vs Chaos element doesn't really take away anything from the Good vs Evil. Or am I just being a whiny old fart?