One further factor that is present in the Old School games that struck me as egalitarian, but which I forgot while writing my previous post, is the presence of rival adventuring parties! Our heroes are not the only heroes under these rules, while at least in 3.x it was a right royal pain to build mid-to-high-level rival adventurers (sufficient to deter many DMs from doing so, self included), and in 4e the complexity gap between monsters and PCs is even larger, and the rules they operate under are so different that I would be reasonably surprised to see a rival adventuring party built under the same rules as the PCs in a 4e game.
This lens has also allowed me to articulate a reason I so dislike Midnight's Hero Paths - namely, that they are essentially exceptionalist. They say "Midnight is a dark and horrible place and it sucks... but you few, you happy few, you get to be awesome, because it's fated." They are counter-thematic. They may serve a useful function in terms of making up for lack of magic items and spells, but that does not mean I have to like them, or that Iron Heroes wouldn't do it better.
Wish fulfilment - someone once wrote about wish fulfilment in new school games, as opposed to world acceptance in old school games (perhaps Brendan when he was still at Untimately?). I recall that whomever it was was challenged about "what are new school gamers wishing for, though?" I believe Brin's hypothesis may provide an answer - the Campbellian heroic demigodhead (I respectfully object to Brin's terming it Nietzschean; it is in some ways, but not in others). To stand head and shoulders above the fellow occupants of one's realm, to be confident and assured in victory, to alter the world to one's will, and to have these be a given as the result of one's mere participation in the affairs of that world.
Finally, holy crap video games are rife with this same strain that Brin sees in Lucas' work. Halo and its relatives all the way back to Doom, the MOBA genre with its towering champions wading through waves of minions, the Elder Scrolls with their prophesied heroes born under auspicious astrology... Hell, I'll be the first to admit that part of the fun of danger-rooms in Dwarf Fortress is that it satisfies the aristocratic impulse by creating a cadre of demigods, individuals within the bearded sea who are picked out and cultivated into unbreakable, indefatigable perfection, without the risk of injury, defeat, loss, and death that combat (required for such gains) normally entails.
It really does all come back to risk and cost. The Halo player is not made to endure the Spartan's training, nor are the physiological, psychological, or social prices of that power brought to his attention as more than a momentary joke. Power is given to him freely, to enjoy as he sees fit, no strings attached except the limited destiny he must fulfil. It is not fought for, and it is not earned, except inasmuch as real money was spent upon the acquisition of the game and hardware (speaking primarily of single-player; the development of skill in multiplayer is another matter).
This, then, is part of the essence of the Old School, to me. Your fate is your own; neither your success nor your failure are predestined. Any success you achieve is by your own luck, skill, and guile, and your failures are the result of your lack thereof. The consequences of your actions are yours to either suffer or exult in. TANSTAAFL; nothing will be given to you freely, but anything you earn, achieve, or build is truly yours, though you will pay a price for it sooner or later. Learn from your failures and strengthen your resolve; improve thyself, eschewing cheap promises of unearned demigodhood in favor of that which is difficult, for that which is difficult will make you a better player of games and a more able human. How can one strengthen one's kung fu, or approach arete by gaming, if excellence is a given without striving? Here is the heart of "player skill" - not meta-knowledge about what types of golem are vulnerable to what types of magic, or that lightning bolts bounce, but the cultivation of ability to rapidly extract data from foreign situations and reach accurate inferences from it, the ability to improvise and repurpose tools to unfamiliar problems, a balance of courage with caution and tenacity with calm acceptance of occasional failure, rational self-interest tempered by loyalty to a group, a healthy sense of suspicion, a healthy ability to trust, accurate knowledge of one's own flaws and limits along with one's strengths, an understanding of and ability to accept risk, the ability to resolve moral quandaries rationally and live with one's conscience, the ability to define realistic objectives and push through to their completion, and knowing when to back off and reevaluate those objectives... Above all, a willingness to experiment, to try, to make the attempt, to push one's own limits, to spit in Death's eye and hope for a 20. Are not these things suitable, meet, well, and proper in a human being? Are these not things that we should pursue in our gaming, if it offers us an opportunity? And should we willingly pass that opportunity by, in order to... what, tell a pretty story and experience a brief and fleeting happiness, made cheap by its predestination and lack of real sacrifice?
... hell, should I be gaming at all, with that sort of mindset? Perhaps I should add "ability to cope with doubt" to the list, exercise off some energy, and call it a night. The joy and curse of freedom is that one much choose.