I agree that what you're saying is true, but in the context of my comment, I stand by the statement that cycles/op is still a more meaningful measurement of performance than seconds.
---
Counter-nitpick .. your statement of "if you put a bunch of other instructions around it" assumes there are no data dependencies between instructions.
In the example you gave:
FloatMul
ADD
MUL
DIV
Sure .. if all of those are operating on independent data sources, they could conceivably retire on the same cycle, but in the context of the article (approximating the performance profile of a series of operations) we're assuming they have data dependencies on one another, and are going to be executed serially.