I'm sure it would be possible to produce a few excellent software developers doing the bottom up approach as well, starting with a course on hardware, then assembly and then going up the stack from there. I would have loved that approach personally, but it would probably turn the average CS student into an awful programmer.
Sure, start the freshman off with Python. Let them get their feet wet and see whether they even enjoy this dark art at all. Besides, knowing about the hardware before "Hello World" isn't very helpful.
After their intro class, you don't do bottom up or top down. You start at both ends and work your way in. You got your computer systems course which teaches C and a smattering of assembly and hardware and your algorithms and data structures class that can use an easier language like (python/scheme) to reduce the cognitive overhead to teach the material.
If the students are taking these at the same time and the professors coordinate to explain how they relate at the various levels, you get very balanced developers. (Assuming they do well in the classes!)
I took a couple classes in college that were designed to teach what is going on underneath the 1s and 0s of instruction sets. I didn't take the classes about how circuits work, but they existed, I had friends who took them, and I really wish I had as well.
Maybe this isn't required knowledge to do software engineering, but it's definitely useful knowledge. Why wouldn't we want to learn these things?
So, virtual functions aren't real because they're just vtables implemented in C. But C isn't real because it's just fancy assembly language. But assembly language isn't real because it's just fancy machine language. But machine language isn't real because it's just 0's and 1's zipping around the hardware. So I have to learn how integrated circuits work before learning how to program? No.
Bottom-up knowledge is important for understanding performance and other trade-offs. However, there's also a lot of benefit in learning how to program in a formal system without knowing much about how that system is implemented under the covers. If I was teaching an intro programming course to undergrads in 2017, I'd be strongly inclined to teach them a clean functional language first (e.g. Elixir, F#, etc.), and only introduce gory details like pointers and memory allocation later on.