Something I've begun to notice as I replay Origins... King Cailan is a maker-damned fool. 

Ostagar is a brilliantly defensible location. Even as a ruin, it's structure has held up remarkably well. The massive walls loom over the valley where he makes his foolish stand just begging to be lined with archers and mages. And Redcliffe forces could have provided backup within the week... during which time a person could have added additional fortifications. There are so many opportunities here and he decides to play the bloody hero.^no ^pun ^intended

Maker's breath, I never thought I'd say it but... 
**Loghain was right.**