I agree with those who have said they like to start higher than 1st to allow more fleshed-out histories and competent PCs. My group generally starts around 4th-6th level for our games, as we view the various level ranges as roughly mapping to 0th level as children, 1st-2nd level as the teenage hero with his father's sword or a magician's apprentice, 3rd-4th level as competent young adults, and 5th-6th level as the average adult. The average adult, then, has finished his or her general education and is able to take a prestige class to specialize, so most character concepts are realizable at game start without needing to worry too much about PrC early entry or the like. 7th-10th is roughly top-of-the-line mortals, 11th-15th superhuman, and 16th-20th mythical beings, so our more party-focused games (e.g. the party is a group of Eberron airship pirates, master assassins, etc.) generally end around 13th and our world-focused games (e.g. stopping a planar invasion, taking over a kingdom, etc.) end around 18th or so.
For my PbP games, I don't think I've run any that started lower than 6th, and most of them start in the 12th-15th range. As veekie said, with most PbP games you stay the same level for a year or more and games tend to die before that, so people like starting off more powerful, or just getting a chance to play at levels they don't usually reach in RL games. One of my games is the exception to that--they started at 8th and have leveled up to 16th over the course of just over two years--but that's a major exception, with a very proactive party with a high posting rate.
I'd add to it, is there a single iconic hero, the sort of thing that would inspire you to play D&D, that is a 1st level character? There is, no doubt, some place for the villagers who grow up to be great adventurers story arc. But, the idea that that is THE arc for a D&D campaign strikes me as a mistake, and more limiting than anything else.
I'd say there are tons of iconic heroes that start at 1st level, including all of the "farmboy with a destiny" heroes that you mentioned, as well as many magic-using heroes, because the audience has to have the magic system explained to them and explaining it to an apprentice protagonist is a good way to do that without an OOC infodump. The problem with that, of course, is that characters in fiction have plot shields (so they don't need to deal with the swingyness of low-level RNGs), and most books end around the equivalent of mid levels (so starting off as a gish works since being a duskblade rather than a fighter/wizard won't hurt you in the long run). Many protagonists start at 1st level, but as you noted,
staying there for a while sucks and isn't very heroic.
The series closest to the D&D model that I can think of is Wheel of Time: you have five low-level PCs coming from a village somewhere after it's attacked by orc-equivalents and everyone they know dies, everyone becomes highly magical as the series goes on whether from spellcasting or supernatural abilities or magic items, the "game" changes as high-level magic comes into play, etc. Hell, the main characters of Ran, Perrin, Mat, Nynaeve, and Egwene even map fairly closely to the wizard/fighter/rogue/cleric/bard roles (well, barbarian more than fighter and more a high-Cha cleric than a bard, but you get the idea). And yet even there the characters aren't 1st level for more than one or two books out of 13+, really: Rand channels (= takes a few levels of wizard) and Perrin becomes a wolfbrother (= takes a few levels in ranger) before the end of book 1, Egwene and Nynaeve start Aes Sedai training (= take a few levels in cleric) in book 2, and Mat starts gaining his past-life memories (= takes a few levels in factotum) by book 3.
So even in the most D&D-like fantasy series on the market that maps the most closely to the hero's journey and "farmboy heroes" thing, the time the heroes spend below 3rd or 4th level would map to maybe one or two sessions, tops, and could more easily be relegated to backstory if the setting didn't need to be introduced.
I use this example because a friend of mine gave Wheel of Time as his reason for wanting to start at 1st level and work his way up, but when I pointed out how fast the characters come into their power, he agreed to start at 5th level like the rest of our group wanted. That's the problem with 1st level, really--it
seems like the right place to start a game, so a lot of people tend to like to start there, but it doesn't work out as well if you spend several sessions there without author fiat helping you along. I liked things better in AD&D, where you spent just a few sessions working your way up to 4th or so, then a bunch more sessions working your way up to 8th, then things plateaued at the mid levels, so you got out of the swingy-lethal levels quickly and spend more time in the "fun" levels.