Errr... what? Megatexture is suitable and was made for large worlds.
While MT is suitable for large worlds, it's not suitable for 'VERY' large world. 128k x 128k pixels texture is not big enough for covering like 10 square miles map. Technically you can, but textures will look too blurry. And this is already one of the technical problem of RAGE.
http://img339.imageshack.us/img339/9703/ragetheshroudedusmp4201.jpg
Where is everyone getting this 15 hour game length. Please provide source.
http://www.computerandvideogames.com/297061/news/rage-lasts-around-15-hours/
Fast travel? Who told you it doesn't exists. Nobody said it does but doesn't mean you disregard it's existence.
http://www.gametrailers.com/episode/gametrailers-tv/117
Tim Willits says there's no fast travel around 11:00 of this video.