Thanks for the comments. I am relatively convinced, but, I have to say, almost all the comments about the downside seem to come from people who haven't had those things happen to them. And if someone did have a chain break, how long or how many miles did they put on them?
On my part, I've ridden some 150,000 miles over 30 years (5,000-6,000 miles a year), and have never had any of the horribles happen to me - - though, admittedly, I've never pushed a chain or cluster all the way to the limits. Nor have I ever heard of anyone even having to replace the chainrings. And, I've ridden up and down hills and mountains (live in the San Francisco Bay Area), in good weather and bad, and ridden aggressively and on multi-day tours. I've let some chains go for much longer than recommended, and, only when I change a chain do I get any negative symptoms.
For example, why would the rear cluster gears, which get used most, wear so fast, when the chainwheel, which only has 2 or maybe 3 gears, never seem to wear? And, I never have trouble with the chain at anything like 1,000 miles - - except I have to change the cluster if I don't change the chain by about that point.
By the way, I measured with a Park CC-3 or whatever, and my chain sat between .75 and 1.0 or whatever the upper measurement is. I put on a new chain, and the highest gears now skip (even though the middle gears on the cluster are the ones I ride most often). Admittedly, the tool is the old version of the chain measurer that Park has . . . guess I'll just break out the ruler from now on.
The way I figure it, if the cost of a cluster is about twice the cost of a chain, you'd have to go through the equivalent of missing two chain changes to come out equal. Also, if you can buy chains off-season at reduced prices, the same holds true for clusters. The biggest trouble is finding the spot where your ride doesn't start deteriorating . . . has anyone ridden a chain so long the shifting isn't very good, or it starts skipping from wear? Also, I have to take the cluster into the LBS for service because I have never mastered switching clusters.
Thanks again, not arguing, just trying to get at the truth.