Confused as to what post you're referring to... but thanks nonetheless!
Working tri's doesn't build good bi's, but it will build good/big arms in general. Think about it - the tri's make up roughly 2/3rds of the arm, so develop them, and you'll have big arms!
Deads work EVERYTHING - literally. They certainly hit lower back, but so much more. Quads and glutes when you're coming up from the lowest position, lower back, glutes and hams at the top/lockout, and upper back, traps, forearms etc. throughout the entire exercise. They may not directly hit chest and shoulders, but it's such a big exercise, everything will grow with heavy properly executed deads.