Failure costs and chances are proportionally lower in larger switches. Member of Audience Historically we did integration by strict layer division. There are issues with the amount of manual configuration required. There is a lot of manual configuration needed for routers, Ethernet switches mostly autoconfigure. Member of Audience Historically the differences between IP and ATM have become divisive even though they don't need to be.
Policy routing decisions in the Internet are the configuration nightmare.
Etherswitches as port multipliers are good, but they are not suited to build whole topologies. Member of Audience Reservation requirements are very hard to take into routing, even ATM doesn't have a solution there. Both IP and ATM are good, the problem only starts when you put these two network protocols on top of each other.