Still, it is always puzzling to me how believers can attribute their escape from calamity to God’s protection without feeling compelled to explain why God did not extend that protection to other people not clearly less deserving than themselves. If God was capable of working a “miracle” to prevent you from death by tornado in Missouri or Alabama, why didn’t he work that same miracle to save your neighbors? (We will leave aside the added puzzle of why God would allow the natural cataclysm to proceed in the first place and confine himself to piecemeal, after-the-fact efforts to mitigate its effects for a select number of survivors.) The implication of attributing one’s own good fortune amid a wave of misfortune to God is inescapable: God cared for me more than for the deceased victims. Yet only rarely does this implication seem to break through into a believer’s consciousness.
I think this response gets both the implications and the psychology quite wrong. There is no particular a priori reason why God would do exactly the same thing for everybody, and it doesn't follow from thanking God for saving one from calamity either that God did nothing for the unfortunate neighbors or that God cared for the fortunate person more -- indeed, as old-fashioned Baptist preachers are sometimes fond of reminding their congregations, it could very well have been the exact opposite: as one preacher I know put it (I paraphrase), God may have saved you rather than them because you need more time and help to escape from hell than they do. Only the good die young, as the saying goes! MacDonald's 'inescapable implication', far from being inescapable, isn't really even implied without making a number of obviously debatable assumptions. MacDonald's implication, in other words, is really based on her own idea of What God Would Do, and the assumption that everyone else has this idea, too; a problematic assumption given that MacDonald is an atheist with a long history of not exactly having a complete sympathy with theists.
But, more importantly, I think she is clearly misreading the psychology of the situation. It is a natural human response, on having survived a great catastrophe, to feel grateful for it. And it's important to note that this is true regardless of whether one has anyone to whom one can be grateful. Martin Gardner has an excellent and underappreciated philosophical novel, The Flight of Peter Fromm, in which this is a secondary theme: gratitude is a very human response, even in situations where there is no human agent responsible; it's a common, although not universal, accompaniment of relief. If you're a theist, you'll feel grateful to God, as the most obvious higher-order agent to whom it could be attributed; if you're an atheist or agnostic (or perhaps a deist who doesn't believe God intervenes, as Gardner was), it might just be a strange sense of gratitude to no one in particular. And it does seem strange to be grateful yet to no one in particular, but there's nothing irrational about it, because gratitude is the human response in which we feel more than merely relieved, and this can be appropriate whether one has anyone to be grateful to or not. The feeling comes first, and sometimes demands expression.
People in general, however religious, tend to be rather agnostic about what they can know about God's purposes; that doesn't change the fact that they feel grateful to have survived, nor does it change the fact that the force of relief can demand that this gratitude be expressed. And the associated feelings don't have any particular connection with each other: you can be grateful for having survived while sad for those who didn't; you can be grateful for emerging unscathed even while bewildered as to why others didn't; you can be grateful for having lived even while anguished that others didn't; you can be grateful and relieved that you got through and feel bad for feeling grateful and relieved. The two sides simply come apart because they have no necessary connection.
Thus there's no particular reason why one should feel compelled to explain the difference -- one might try, in order to satisfy one's curiosity, or in order to relieve one's anguish or guilt, but there's nothing that positively demands that one do so. It's entirely possible just not to know, and even to believe that one can't know; the motivation for expressing a thank-God will still be there, utterly unaffected by one's agnosticism about God's mysterious ways. This is not the solipsism of faith or of anything else; it's simply a case where motivation does not depend on what one knows or what one doesn't, and where (what is more) the rationality of the motivation doesn't depend on what one knows or what one doesn't.