The passage you quote was written a few years ago and I've refined my thinking somewhat since then. I was really aiming it at people who get obsessed with more complex forms of ornamentation such as rolls and crans of various kinds before they can make sense of a simple tune - and I have come across plenty of such players of whistles and other instruments in real life and on the net. In that respect I stand by that passage.
Now however I would say that more basic devices that are commonly lumped under the heading of "ornamentation", especially cuts and to some extent taps, are indispensable and should be integrated into your learning of Irish music almost from the word go. If you don't learn them early you'll probably develop the habit of tonguing all over the place, a habit that is hard to undo once you've developed it. These devices then are not less important than good rhythm because they are more or less vital to developing good rhythm.
This is interesting to me, because once again I find what Steve writes lining up with my own gut instinct. I've learned a couple of tunes and am working on a third. Playing the same tunes over and over again gets a little tiresome, due both to repetition and the fact that my playing isn't quite as interesting to listen to as some of the CDs I own. I could start learning some new tunes, but that wouldn't necessarily make me a better whistler.
Another way to make practice more interesting, though, is to throw a new challenge into the mix. As I mentioned last time, Sheebeg Sheemore is a tune which really does benefit from cuts in a few places, and I tried that tonight. It's not so hard to play the cuts where I would normally tongue a repeated note, and it helps keep my mine focused on the tune.
I'm grateful to everyone who responded, because all of this is really helping to condense my thoughts about how I need to practice, what I wanted from the tutorials, and what I'd like to do with this weblog. In summary, I want to pass along useful advice from the point of view of a beginner, since most books seem to be written by experts.