@Pyro: My guess as to why so many people level as ranged specs is because of the downtime issue. Yeah, with full heirlooms it's not an issue at all (particularly running double caster trinkets). But especially before the big revamp, most caster classes had you drinking like Charlie Sheen on a bender. For the classes you cited, the caster spec is perfectly viable, but even with heirlooms you still come out faster going melee. Granted, the spec that's most fun for you will always be the best one to level as, but most people go for pure efficiency, so they go with whatever has the least amount of downtime that kills stuff the fastest, which is generally going to be a melee spec.

Also, elemental at least was horribly goddamn boring prior to 4.0.1. All you did was LB spam your way to 80, with the occasional shock tossed in. Even frost mages got more to do (especially having actual AoE). Not getting a second viable spell until 75 was unbelievably shitty. Elemental also lacked insta ghost wolf unless you gimped yourself dipping into the enh tree, and even now doesn't get until you start hitting Cata content, which means you also miss out on a movement increase for about 80 some-odd levels.

It could also just be an issue of aesthetics or personal preference. I have a complete set of heirlooms, including cloaks and two sets of trinkets, so I could basically do whatever I wanted for my troll druid. I loved the balance druid playstyle and messed around with it once I got dual spec, and even went balance/resto for dungeons. Then I hit level 29. I tried boomkin out for about 5 minutes, decided I absolutely detested everything about the form (not to mention having to shift out to use a mount), went back to kitty and haven't looked back. Yes, keeping a set of caster leather in my bags when I want to heal dungeons is annoying when my main spec is kitty, but not nearly as annoying as dealing with a giant orange chicken.