We went around that mulberry bush already a few months ago. The response from WotC was this:
http://community.wizards.com/dndnext/blog/2012/05/18/paladin_design_goals
Their big bullet points:
1. The paladin is a champion of a divine calling.
2. A paladin can see and smite evil.
3. A paladin is a fearless and selfless warrior.
4. A paladin has divine abilities.
#3 is the overlap with the Fighter.
#4 is the overlap with the Cleric.
To keep the Paladin from being a Fighter/Cleric they need to do two things major things. First, they need to put the core of the class into items #1 and #2 on the list. Next they need to make the points of overlap in #3 and #4 be more distinct mechanically from how the Multi-Class build would play out.
To me, that means not dipping into the Fighter's expertise system for things Smite could handle (like Damage Escalation) and making sure most of the Cleric spell-list is unique. A character defined just by fusing those two things is the Fighter/Cleric and should be distinct from the Paladin from low-earth orbit. It might even mean making Paladin-only spells/prayers that support his mechanics. Focus on short-ranged combat-enhancing magical effects that smite or protect and you'll have a paladin class that could include the avenger too.
- Marty Lund