This is very nicely done. I do think it has one major omission -- something that is unfortunately omitted all too often. This is that, just as we get to decide

This is very nicely done. I do think it has one major omission -- something that is unfortunately omitted all too often. This is that, just as we get to decide what "n" means, we also get to decide what operations we are counting. Furthermore, our choices matter. For example, if we are dealing with data accessed via a slow connection, or just about any kind of distributed system, operations that use the slow connection will be much slower than those that do not. So often we will count only those. O(n^2) doesn't give the full picture, if we only use O(n) slow operations. For another example, if we are doing computations using large integers, then it usually does not make sense to count arithmetic operations as single operations. In such circumstances, a large-integer multiply can take a lot more time than a pointer dereference.