Keith is right: "normal wear and tear" can have many interpretations and sometimes can go to arbitration for definition: I once had a tenant who would shut all water faucets overly tight until he would eventually break all seals and have running water everywhere. I have repaired faucets many times until I finally presented him with a repair bill at which point he paid and the faucet leaks stopped.
I had one woman tenant who would dump her long hair, Bounty paper towels and cat litter in the toilet until it not only wouldn't flush but when clogged, she continued to flush the toilet thinking several flushes would eventually unclog it but instead it would flood over. Like, Duh! that is not wear and tear.
A friend rented his house that was newly remodeled including a fancy glass cooktop stove. The tenants ruined the glasstop because they would clean the glass top with comet or other strong cleaning dÃ©tergents.
I think landlords should include a specific clause in their leases to specisically define "normal wear and tear".
Unfortunately, it seems that the majority of tenants think that their landlords are making money off them; therefore, they don't have to respect their landlords properties.