"Hertz" just means "per second". It can be anything per second, there are no units in the numerator. It just a measure of frequency, anything per second.
If anything you are counting is happening 14.4 million times a second, then that thing is happening at 14 megahertz. It's just a unit. If there are 14.4 million writes per second, then the writes are occuring at 14.4 mega hertz. That's just the definition of hertz.
And in their test, they made writes at that frequency, right?
It is, however, commonly used for average frequency rates too, not just measurements of constant frequency. "Frequency" the word means how frequent something happens, right?
I don't know what the 'something' to measure frequency of in pink noise would be, but if there is something to count over time, you can measure it's frequency.
However, it is true that "In some fields, especially where frequency-domain analysis is used, the concept of frequency is applied only to sinusoidal phenomena, since in linear systems more complex periodic and nonperiodic phonomena are most easily analyzed in terms of sums of sinusoids of different frequencies." In some fields.
I have no idea why we're arguing about this except that we like arguing on the internet though.
http://en.wikipedia.org/wiki/Hertz
If anything you are counting is happening 14.4 million times a second, then that thing is happening at 14 megahertz. It's just a unit. If there are 14.4 million writes per second, then the writes are occuring at 14.4 mega hertz. That's just the definition of hertz.
Haha, Google agrees, check it out: https://www.google.com/?q=4+per+second#q=4+per+second