Wow. People are still using Tiger. Why?! Haven't they heard of Leopard? 10.5.2!!
1. If its being used in a corporate environment
2. Tiger is good enough, why bother with Leopard
3. Don't have a capable machine
4. Don't see the point in upgrading / not interested
5. Isn't compatible with some software a person may be using
6. Perceive Leopard not being stable enough ( also see point 1 )