Nature Priests
The point that I think people miss is that Druids are Nature Priest(esse)s. Their weapons and armors are all special, in order to reflect this...
They can wear only padded, leather, hide, and wooden armors, and use only wooden shields. Note that the PH has a spell (Ironwood) which mentions wooden plate!
Likewise, their weapons (since first edition) are supposed to represent natural weapons... They refuse to use "metal raped from the Earth", relying on meteoric iron, wood, stone, etc.
Why a scimitar and sickle? Because they represent the horned moon (special to Druids). If in an Oriental campaign, Druids could probably use Katannas, too. You may see the flavor as "silly", but that's where it comes from.
Other weapons based upon nature include the dagger and dart (based upon thorns), the club, staff and spears (based upon trees), scimitar and sickle (based upon the moon), and sling (based upon both animals and rocks). Now if I were doing things, I'd limit them to sling stones, only, but let them do 1D4 with no to-hit penalty, and disallow lead sling bullets doing 1D6. I'd also allow them to use the Morningstar and Greatclub, so long as they didn't incorporate iron (but that's just me).
As for bows and crossbows, no. The only arguement that I can see for this is the shooting rays of the sun... and I'm not buying that. If you want a bowslinging Druid, play an Elf, or take Fighter/Ranger levels, and work out the spells thing with the GM.
In first edition AD&D, they could use only leather armor, but were also allowed the hammer as a weapon. When Unearthed Arcana came out, they were allowed to use Padded, as well as the new weapons Aklys, garrot, lasso, sap, staff-sling, sword (khopesh), and whip. Of these, only the sap and whip have survived into 3e. Note that they were disallowed use of the blowpipe, even back then!
I have more trouble understanding why they can't use such weapons as the Falchion (curved), Greatclub, Morningstar, Sap, and Whip than the bow, but assume that it is a game balance thing... Most of their weapons do 1D6 or less, so I can understand disallowing the two handed weapons. The rest, though...
In any case, I don't see how the bow (or more especially the crossbow) fits into the Neo-Celtic image (if you have the 1e PH, read the description of the class given there).