Used by which remote controls? Many cheaper universals can send only on the frequencies that are the most commonly used and cover about 95% of consumer IR devices, but it's not at all rare to find an IR remote-controlled device that operate a little outside those common bands, especially from smaller or newer manufacturers, and those universal remotes won't work with those devices. While a better (and more expensive) universal remote does. I have run into that myself, personally, with some obscure branded devices. A cheap universal I have couldn't learn their signals, while my more capable universal could lean them, as well as upload the hex codes for those IR signals to my computer for duplication on other capable remotes.
And "keys versus macros" was simply an example of signal length and complexity. Cheap remotes often only handle short, simple sequences while more capable remotes can handle more longer and more complex signals, including pauses. Not that you need specific signals for this application... just an open keyline.
So, the problem is simply that the IR signal involved is outside of the receive/transmit band of the specific universal remote he used. But that does not mean it is outside the receive/transmit band of every universal remote ever made, which the writer implies. The writer made an expansive, definitive statement based on a single example. If, by chance, the writer had used a better remote he might have made an expansive, definitive statement that universal remotes do work for this, and been equally wrong. Because some can work, and some cannot.