When I began to plan how I wanted to convert "Dragons of Despair" from the AD&D rules to the 4E rules, I thought about whether I should take a top-down or bottom-up approach in detailing the setting of the adventure.
As world-builders know, a top-down approach to designing a milieu involves starting large and considering the big picture. Which PC races exist in your world, and how to do the various classes fit in? Are there new races or classes that need special rules? How about organizations that would work as paragon paths? What are the populations and dispositions of the cities, towns, villages, and nations of the world? Who are the rulers, movers, and shakers?
A bottom-up approach, on the other hand, involves starting small and working on only what you need. Are the PCs going to visit Town X? If not, then you don't need to spend much time thinking about what Town X is like, who lives there, and what the current situation is there.
Ultimately I decided that I was going to treat my conversion like an adventure path and not a campaign setting: I was going to use a bottom-up approach. In truth, the result is probably more like a hybrid of top-down and bottom-up because the Dragonlance setting has existed for many years; all the conceptualization has been done already. So although I didn't spend any word count on detailing the town of New Ports, for example (since the PCs won't visit it in DL1), the information about this location is out there somewhere.
I think one of the benefits to treating Dragonlance like an adventure path rather than a campaign setting is that it allows me dispense with designing fiddly rules bits for "Dragonlance-isms". I was content to let the existing architecture of 4E fit where it needed to fit. For example, I might have designed a new PC race: the kender. They'd probably have a racial power called "Taunt"; maybe this power would mark one or more foes or have some other effects, like pulling them a few squares. It'd be neat. This approach would be expected if Dragonlance were given a full treatment as a campaign setting, but for an adventure path, is it really necessary? Why not just use halflings straight out of the Player's Handbook? Likewise, why bother with rules that attempt to give mechanics to exactly what it means to be a Wizard of High Sorcery? In the context of an adventure path, who cares?
I think that the original Dragonlance modules took this approach too. There were a few corner cases (if I remember, they added some special rules for kender) but for the most part, sure there were Knights of Solamnia and Wizards of High Sorcery and Silvanesti elves and dark dwarves and whatever else -- but these were just names that fleshed out the milieu in the imaginations of the players. They were story elements. There was no mechanical difference between a Silvanesti elf and a Qualinesti elf or between a White Robe wizard and a Red Robe wizard.
Conversely, because I'm treating the conversion project like an adventure path and not a campaign setting, I don't need to bother explaining 4E-isms that don't seem to fit easily into the established milieu -- like dragonborn, tieflings, or eladrin. Are there tieflings out there somewhere in the wider world of Krynn as it's depicted in my version of DL1? I don't know -- maybe. But since there are no tieflings in DL1 I didn't feel compelled to explain their presence or absence.
It wasn't until the Dragonlance Adventures hardback was published for AD&D that Dragonlance began to be treated as a discrete campaign setting. That book introduced rules mechanics to address the differences between Knights of the Rose and Knights of the Crown, gully dwarves and hill dwarves, and many other Dragonlance-isms. There was even a chart that showed the mechanical influence of the phases of the moons on the spellcasting ability of wizards.
3E really ran with the idea that in-game distinctions should also have mechanical ramifications for characters, as is particularly well illustrated with the abundance of prestige classes that were developed. Dragonlance received a 3E campaign setting treatment that introduced races, feats, prestige classes, and even some base classes specific to the world of Krynn.
I think with 4E, we're seeing a return to the concept of keeping story elements and rules constructs largely separate. That is to say, in 4E, rules elements have stories attached, but story elements need not have rules attached. Flint was a metalsmith and a woodworker? In AD&D, it said that on his character sheet, whereas in 3E, he had levels in the expert class and spent skill points in Craft (Metalsmithing) and Craft (Woodworking). In 4E it says "Flint is a metalsmith and a woodworker" on his character sheet. Is one way better than the other? I think the answer to that question is no, neither method has more intrinsic value than the other. One is a more simulationist approah, and one is a more narrativist approach. They are both equally valid.
But because 4E significantly downplays a simulationist approach in favor of a gamist approach (with some narrativism), I decided to go for a bottom-up, gamist/narrativist approach for my conversion project. I think it works.
And that's why you won't see any races, classes, or paragon paths in "Dragons of Despair" or any of the other Dragonlance modules I convert.