Think about it:
1. They're both lonely outcasts. 2. They're both mopey young girls. 3. They're both in their teens. (I've heard Luanne is 18). 4. They both had one-trick pony boyfriends. 5. They both get laughed at and put-down by their classmates 6. They're both into 'beauty' stuff. 7. They both have goofy parents. (Luanne: Leanne Meg: Peter.) 8. They both go to school. (Meg: High school Luanne: Beauty school, but soon to go to college. Like in last Tueday's episode.)
If Luanne and Meg ever meet each other, they'd get along great! :)