It also should be noted that in order to get the 3,000 hp, the British Rail Class 55 "Deltic" used a truly novel design for the prime mover:
" onclick="window.open(this.href);return false;. English Electric, I have read, thought about trying to market the Deltic to the Canadians, but nothing came of it. That locomotive has a reputation in the UK and is very celebrated, much the same way the we have nostalgic love of say the UP Turbines here. The Napier Deltic prime mover was troublesome to say the least, the paired down version in the Class 23 was even more so, and lead to that type having a very short service life. The Class 55 served well, and were only replaced by high speed trains in the 1970s, but they were top-flight brass, and got the utmost of care to help them along.
British railroading is very different than American in their view of passenger transportation. Even today, with Amtrak posting record numbers, a "busy" American station in a mid-sized city can at best hope for only about 10% of the traffic in a comparative UK one. During the period of nationalization under British Rail, labor costs were often overlooked while in the US at the same time were always seen as the bane of the railroads. As such, the Brits fielded many more high-labor locomotives than we did, and were quicker to adopt the new and novel in everyday service.
Add to this the economics of EMD at the time of the E8's creation. Say you were the staunchly-conservative Pennsylvania, and needed 6,000hp for a fast streamliner, It'd be just as easy to put an A-B-A of E8s on the front as it would be to put an A-A configuration of 3,000hp engines. In fact from the railroad's perspective that might be better. If a unit died in route it still would probably be possible to limp in with 4,000hp instead of only 3,000. Now if you're EMD, that need for 6,000hp is happier for you as well, because it means selling an extra unit which means more income too. Proven power, rugged, and easy to service and cheap gets the job done in American railroading.