No, it happens frequently. Even in the last LotR movie, Gandolf seems to think he's about to die while fighting troops, and that's after he's defeated the Balrog and came back even more powerful than before.
When Strider is tracking the hobbits down with Gimli and Legolas, they get surrounded by mounted riders. Sure, Legolas could have gotten a shot off first, but they were obviously in a terrible situation.
Jamie Lannister, basically the best swordsman around, is overwhelmed by troops and captured.
When Rand al'Thor is training against four men, he gets on hit on each, but the last one hits him in the head. He routinely takes on the Forsaken.
This is not uncommon by any means in fantasy.
I would point out that Gandalf and Rand are the only mid- to high-level characters among those examples, and both of them are only threatened at all because they're holding back. Gandalf isn't using most of his power to avoid attracting the attention of the other people in the world who
are a real threat to him (and because Iluvatar nicely asked him not to). When Davram Bashere tries to stab Rand to prove a point--that Rand hasn't been really keeping up with his practice, and shouldn't be anyway because he has better options--Rand stops and disarms him without even having to take the time to think about it.
Those high level characters being "threatened" by mundane threats are akin to saying that a D&D planetar isn't actually powerful because Pelor will smite any angel that tries to use its supernatural abilities, or that a 15th-level wizard is trivial to take out as long as you have either an
antimagic field or 13 12th-level wizards working together. Yes, if you have a high-level caster not use any of his magic for personal protection or offense, low-level threats might affect him, but that's exactly the problem: most fiction deals with what would be low-level characters in D&D, and any high-level characters are usually holding themselves back.
A common argument to see on forums is the following:
"Casters and noncasters should be equal. Noncasters take out casters in fiction all the time."
"Nuh-uh! Magic is inherently superior!"
"Nope, Gandalf and Thoth-Amon and so on are just higher-level than Aragorn and Conan and the rest!"
It goes around in circles after that, but the latter sentiment is closer to being right: main villains are end-game bosses because they're higher-level and heroes tend to be at a disadvantage because underdog stories are classic, not because wizards are better than fighters in the source material. If you look at most fiction that ends up with the hero facing down a drastically stronger foe against which he's at a disadvantage, you'll notice that it almost always occurs because the hero outsmarts the villain (which works because power is not always proportional to intelligence) or because he takes advantage of a special weakness, whether or not it's built in to the magic system or the villain. The corollary to those stories is that the hero has to do it himself because
brute force by bunches of mooks just doesn't work. The Witch-King gets taken out by a "puny" woman and hobbit duo only because of a glaring weakness and his misinterpretation of that weakness. The Emperor is taken down by Vader because Luke manages to turn him back to the light, which Palpatine never saw coming. Wheel of Time channelers are only taken down by the equivalent of antimagic fields, whether it's forkroot tea or 13-women circles or steddings or whatever else.
Any number of men or elves who go up against the Witch-King flat-out
die. Any number of Rebel troops who go up against Vader flat-out
die, and even the heroes get captured easily. Any number of Aiel who go up against a Forsaken flat-out
die. The only equalizer for lower-level characters is trickery or knowledge of a hidden weakness, and "a dozen bandits with crossbows" just isn't that kind of weakness for higher-level heroes. In fact, if we really want to talk about source material, any game which
does have Jedi Master Luke threatened by generic stormtroopers and TIE fighters is contradicting the source material as much as a game that has Gandalf able to mow down the armies of Isengard and Mordor single-handedly.
And that's what the different level ranges are
for. Farmboy Rand al'Thor and Farmboy Luke Skywalker are low- to mid-level, and still threatened by a dozen bandits with bows or a squad of stormtroopers. Dragon Rand "Lews Therin" al'Thor and Jedi Master Luke Skywalker are mid- to high-level, and just aren't threatened by them anymore. And that kind of growth has always been part of D&D. Perhaps not to the same extent, as different editions have handled high-level and epic/immortal play differently, but even in the very earliest editions PCs started off scrabbling for every advantage they could get and worked their way up to being awesome at mid-to-high level. Back in the day, most NPCs were assumed to be 0th-level, and fighters could attack 1 0th-level opponent per level per round, so 6th-level fighters (which, again, is roughly at the point where AD&D and 3e characters first start surpassing real-world limits) were seriously expected to kill 6 people per round, and those half-dozen bandits would find their numbers halved if the fighter's side rolled well on initiative and completely wiped soon thereafter if they didn't run away.
Yes, characters have less health and fewer protections in AD&D, and yes, 4e builds in a lot of safeguards to protect PCs, but at the end of the day the relationship of low-level characters to mid-level PCs has always been "oh yeah, low-level people, they're those things that the PCs either ignore, order around, or slaughter as the mood strikes them." Mid-level heroes of every edition slay gods, take over nations, planes-hop, and otherwise do larger-than-life stuff on a daily basis. When you can take on a half-dozen glabrezu for breakfast, or as Incenjucar said wipe a colony of illithids before lunch, a bunch of bandits have to go waaay out of their way to qualify as a threat.
In 2E this was only true for wizards. 
