Learn English – the origin of the phrase “War never changes”

I'm still checking for the origin of the phrase but here's something from Urban Dictionary:

Self explanitory [sic]. Used as a response to when something of naught value has happened

"News reporter: After the assassin finished off his rampage of brutally murdering The Jonas Brothers, he proceeded to then hijack Mel Gibson's private jet, where they were forced to crash land in the pacific ocean. And nothing of value was lost."

and here's an explanation from Yahoo Answers:

I don't know, but there is an episode of the Critic, in which Jay Sherman says something similar after watching a float of a horse's *** on fire roll into a theatre where the musical Cats is playing.

Okay, found something more scholarly - in page 120 of David Archard's Philosophy and Pluralism by Lord Bhikhu Parekh we find this:

It actually references Aristotle's Nicomachean Ethics (1984), X.7! We're a bit closer now and I found this quote from that same reference:

Nichomachean Ethics X.7

There may be something similar in Metaphysics, but I don't recall that text as well.

"But we must not follow those who advise us, being men, to think of human things, and, being mortal, of mortal things, but must, so far as we can, make ourselves immortal, and strain every nerve to live in accordance with the best thing in us; for even if it be small in bulk, much more does it in power and worth surpass everything."

Almost but not quite. If you read along though - you'll find the closest phrase to "and nothing of value was lost":

So if among virtuous actions political and military actions are distinguished by nobility and greatness, and these are unleisurely and aim at an end and are not desirable for their own sake, but the activity of reason, which is contemplative, seems both to be superior in serious worth and to aim at no end beyond itself, and to have its pleasure proper to itself (and this augments the activity), and the self-sufficiency, leisureliness, unweariedness (so far as this is possible for man), and all the other attributes ascribed to the supremely happy man are evidently those connected with this activity, it follows that this will be the complete happiness of man, if it be allowed a complete term of life (for none of the attributes of happiness is incomplete).

Here it is in the original Greek:

εἰ δὴ τῶν μὲν κατὰ τὰς ἀρετὰς πράξεων αἱ πολιτικαὶ καὶ πολεμικαὶ κάλλει καὶ μεγέθει προέχουσιν, αὗται δ' ἄσχολοι καὶ τέλους τινὸς ἐφίενται καὶ οὐ δι' αὑτὰς αἱρεταί εἰσιν, ἡ δὲ τοῦ νοῦ ἐνέργεια σπουδῇ τε διαφέρειν δοκεῖ θεωρητικὴ οὖσα, καὶ παρ' αὑτὴν οὐδενὸς ἐφίεσθαι τέλους, καὶ ἔχειν τὴν ἡδονὴν οἰκείαν αὕτη δὲ συναύξει τὴν ἐνέργειαν, καὶ τὸ αὔταρκες δὴ καὶ σχολαστικὸν καὶ ἄτρυτον ὡς ἀνθρώπῳ, καὶ ὅσα ἄλλα τῷ μακαρίῳ ἀπονέμεται, τὰ κατὰ ταύτην τὴν ἐνέργειαν φαίνεται ὄντα· ἡ τελεία δὴ εὐδαιμονία αὕτη ἂν εἴη ἀνθρώπου, λαβοῦσα μῆκος βίου τέλειον· οὐδὲν γὰρ ἀτελές ἐστι τῶν τῆς εὐδαιμονίας

There's a French translation of this at Hodoi Electronikai:

Si donc, entre les actions qui sont conformes à la vertu, celles d'un homme livré aux travaux de l'administration et de la guerre, l'emportent par leur éclat et par leur importance, mais ne laissent aucun moment de loisir, tendent toujours à quelque but, et ne sont nullement préférables par elles-mêmes, tandis que l'activité de l'esprit, qui semble être d'une nature plus noble, étant purement contemplative, n'ayant d'autre fin qu'elle-même, et portant avec soi une volupté qui lui est propre, donne plus d'énergie (a nos facultés); si la condition de se suffire à soi-même, un loisir exempt de toute fatigue corporelle (autant que le comporte la nature de l'homme), et tous les autres avantages qui caractérisent la félicité parfaite, sont le partage de ce genre d'activité : il s'ensuit que c'est elle qui est réellement le bonheur de l'homme, quand elle a rempli toute la durée de sa vie; car rien d'imparfait ne peut être compté parmi les éléments ou conditions du bonheur.

Google Translate gives this back-translation:

If, therefore, between actions that are consistent with virtue, that of a man given to the work of the administration and the war outweighed by their brilliance and their importance, but leave no leisure time, tend always to some purpose, and are not preferred by themselves, while the activity of the mind, which seems to be of a more noble, as purely contemplative, with no other end than Similarly, and bearing with it a pleasure of its own, gives more energy (to our schools), if the condition is sufficient for himself, a hobby free of physical fatigue (as far as the nature of the behavior man), and all other benefits that characterize the perfect bliss, are sharing this type of activity: it follows that it is really the happiness of man, when it has fulfilled all the period of his life, for nothing imperfect can be counted among the elements or conditions of happiness.

UPDATE: I was able to contact David Archard and I asked him which particular part of X.7 is the statement "and nothing of value was lost" referring to. He said it was used by one of his contributors - Bhikhu Parekh.

It was used by one of the contributors to a collection I edited – Bhikhu Parekh

okay, contacting Lord Bhikhu Parekh now ... :)

The Online Etymology Dictionary gives the following origin:

blue moon
1821 as a specific term in the sense "very rarely," perhaps suggesting something that, in fact, never happens (cf. at the Greek calends); suggested earliest in this couplet from 1528:

Yf they say the mone is blewe,
We must beleve that it is true.

Though this might refer to calendrical calculations by the Church, so that the general sense of the term and the specific one (commonly misinterpreted as "second full moon in a calendar month," but actually a quarterly calculation) are difficult to disentangle. In either case, the sense of blue is obscure. Literal blue moons do occasionally occur under extreme atmospheric conditions.

So as you suggest, its origin could be either poetic or astronomical. Perhaps the latter inspired the former? A lot older than I would have guessed, in any case!

As for alternatives, the most obvious one is simply "[very] rarely". A more interesting one is "black swan", which can be used to describe a very infrequent event.