Very good points, and I think this illustrates exactly the point here.
The MacBook Air isn't going to be all things to all people; but it expands the available portable Mac options with a third option that Apple hasn't had in a while (and especially not a laptop in the 3 pound range).
It seems like some people are looking at it, seeing it doesn't meet their own deeds, and deeming it to be unnecessary or stupid or not suitable for anyone.
But this isn't the case. It has its own strengths and weaknesses, just like Apple's other machines and many other manufacturer's systems.
No machine is 100% perfect. I've seen so many comparisons to the TZ (natural of course given that this is what Jobs used as the comparison in the keynote), but the TZ is not the end all be-all either.
I personally had considered a TZ for quite a while, but I found the screen to just be too small for me, and the keyboard to be just too tiny to comfortable type on. I owned an SZ for a bit, but had issues with it as well (didn't like the keyboard, and some other things).
Is the MBA perfect? No, of course not. But I think it makes for an interesting third portable Mac option, and the compromises it makes are not compromises for those who don't need those options; I've rarely ever used the optical drives on most laptops I've owned in recent years. One of the other laptops I'd been strongly considering was the ThinkPad X61, which has widely been praised, and is also an optical-drive-less machine. The X61 has an absolutely amazing keyboard, but it also has a pretty mediocre screen.
I think Apple has done a nice job here, and added a nice option to their product lineup that gives Mac laptop buyers another option to consider. For some people, the MacBook is more than fine. For others, the MBP is the right choice. But it's not hurting anyone to have the MBA as an option too.