I don't think one means the other. it comes down to preference, and more people seem to prefer the things that level range offers.
Things like the game actually working better?
Like what some people have been saying: "starting to get some neat abilities, but don't have to worry about being uber powerful." and "I've played this archetype for a while, and I'm anxious to try out another one."
Those could both point to something in the nature of the system. D&D classes accumulate new abilities as they level. You go from not having much to do, to having interesting new things, to getting bored with the old things and overwhelmed by the sheer numbers of new things you've accumulated. For instance, if you started with more abilities at first, but could trade out those that got boring for newer ones as you leveled, characters could have more longevity across levels. You'd start with 'neat abilities,' never worry being 'uber powerful,' and the archetype wouldn't get old so quickly.
Think of it like this. Compact cars far outsell offroad SUVs. That doesn't mean SUVs have a design flaw. That just means it offers a different experience.
Offering a different experience doesn't mean they don't have design flaws, either. ;P
Roll-over crash tests, OTOH...
If this poll is similar to the metrics WotC have at their disposal, it gives a pretty strong indication why WotC might've chosen to only make their APs go up to level 15 and why they also haven't provided any "epic level" adventure stuff yet. The market for it just isn't there.
Heh. Chicken-and-egg, problem, though. D&D has mostly had a mid-level sweet spot. 5-9 in this case. High level is obviously still be problematic, 1st is pretty awful, IMHO, though I may just be running too much of it (thanks to running introductory games & the Encounters format). In 3.x, the sweet spot was 1-10 or E6 variant. Earlier than that, it's fuzzy because classes progressed differently, but pretty nice by 3rd, and pretty messed up by 'name level' (9th or so depending on class).
I said 5th to 9th, but really it's 5th through 20th. 4E was the only edition that I liked playing 1st level.
I used to say that 3rd was when AD&D finally got fun, and 3.0 1st-level felt enough like AD&D 3rd level to be fun, so I'd credit both 3e & 4e with being more playable at the lowest levels.
I agree with the implication (even if you didn't mean to imply it) that the main reason so few people are voting 1-4th is because it includes 1st. 2-4th or 3-9th would probably get plenty of votes.
The design of the exp tables really speaks volumes, too. Progress is fastest (ie the exp it takes to reach the next level compared to the exp budget of the encounters you can handle) the first 2 levels (a single standard adventuring 'day' of 6-8 medium-hard encounters is all you need to go from 1st to 2nd or 2nd to 3rd) and starts slowing at 3rd, dramatically at 4th, it speeds up again once you hit 11th.
Seems like a clear intent to prolong exposure to a 'sweet spot,' and that spot seems to be 4th-10th.
Which encompasses the 5-9th that's winning the poll so handily.