Keep in mind they are not as many cubes either. 6.4 L =390cu in 6.1 =370. So, above SB size, but barely what the old big blocks were. I think it has a lot more to do with cylinder layout though. The new ones are probably engineered more precise and don't need the BIG block.
yeah - guess I just never thought about it... again, the old school brain just equates Hemi with a BB... now ya'all got me wondering about a 6.4L Hemi Scamp....