iBGP or IGP in this design?

Question:

According to this example Cisco 3925E from official CCNP book, the BGP design calls for making the packets flow over the route as shown.
And according to that book, two actions must take place for this design to work:

Make BGP specify a prefix as being best reached through a particular link (BGP PA settings). I'm fine with that, no questions here.
Need to run BGP between multiple routers. E1 and E2 must communicate BGP routes using iBGP connection and because packet forwarding between E1 and E2 goes through other routers (such as Core1 and Core2), those routers also need to run BGP.
Here is my question:

Instead of running iBGP on non-enterprise routers, can't we just add IGP to Enterprise routers and have them to redistribute their eBGP learned routes into IGP, forward them to enterprise network and leave the non-enterprise routers running IGP?

Answer:

i totally agree with you. An IGP (OSPF,EIGRP or IS-IS) would be even more flexible in this scenario that otherwise in the near future can represent some scalability problems should you add some routers more due to the fact that no BGP route reflectors are in place. If the Joseph guessing is right (you have a lot of prefixes) just use summarization and you will definitely see benefits in your design. Except for SP environment, iBGP should never be extensively deployed in an enterprise. You you want a more valuable opinion about this topic, Jeff Doyle (TCP/IP Vol 2) makes clear why we use BGP and ...it is very interesting Cisco3925E  For more info, please refer to http://lilirouter.soulcast.com/