Hi Lakhwinder
As per my understanding redistribution of Default-Route is not allowed into OSPF/ISIS/BGP routing protocol and we have mechanisms of injecting default-routes in each routing protocol such as EIGRP/ISIS/BGP. So here when we are redistributing the default-route of NAT Device pointing towards Internet Router into EIGRP Process same is being picked and shown up on PE1 under VRF Specific EIGRP Process but further when EIGRP is being redistributed into MP-iBGP process the default-route is not being picked up.
In order to propogate a default-route for the Particular VRF within the MP-iBGP cloud we need use the network 0.0.0.0 0.0.0.0 command or default-information originate command under the address-family ipv4 vrf for that particular VRF and then it will start sending the default-route it has learnt from the NAT router into the MP-iBGP cloud and any other VRF Specific eBGP neighbours.
A very good link for your reference
http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/L3VPNCon.html#wp321598
Hope this helps to provide some insight into your query.
Regards
Varma