"Why bothering with textures when bots have access to the whole map data ?"
Right. All you really care about is "Can I walk on this surface?". It becomes more complicated when you have surfaces that you CAN walk on but probably don't WANT to walk on (like lava, or water). Then you have the problem of connecting two surfaces that are walkable, but don't have a walkable route between them (such as areas where you have to jump from one surface to another or areas connected by ladders, lifts/elevators, etc.).
Navmeshes are a great way to have the bots be able to navigate on ANY map without having to go to the trouble of placing waypoints for them to use to navigate.
You can find many good links on "navmeshes" or "navigation meshes" by searching for them on
www.google.com
Also the "Game Programming Gems" books and the "AI Game Programming Wisdom" books cover this topic.
botman