I think they will be rideable in town. First off, the town and area outside the town are not seperated in 2 different zones like in ffxi. Second, the stables are in the center of the city.
Lastly unles ffxi, where you had a stable building with a path leading outside or a tunnel if you thinking norg. there isn't anything like that. Since we had a mini cs when we rode out on the choco.

I really have no issue seeing chocobo riding in the city. I think it is a cute concept. I liked riding my Mount in WoW with in the city. It made them feel like cities.