I'll ignore your emotional outbursts, Peter, and instead address the facts. What is your objection specifically? Did you read this as "typical mountain bikes have 21 speeds"? If so, read it again.... I gave a range of teeth reasonably typical of a 21 speed setup. Who in this industry defines "typical"? You think I'm off by a couple? Big deal. Get a life. Every cluster is different. And if you don't like what the manufacturer provides, drill out the rivits on two clusters of the same series, and assemble your own with spacing you like. Any way you cut it, however, you will still have substantial overlap and redundant selections as you cycle thru the combinations.

Gearing is not rocket science, yet it confuses many bike buyers and riders. Lets remember that you opened the discussion with calling higher gear count "marketing", and ignored the basic "I want to understand this" request of the original poster. At least some of us are making an earnest attempt to help out a fellow rider who is bold enough to ask an honest question.

End of discussion......

Would this not depend on the age of one's mountain bike (mine's old enough to vote :) ) and on one's inclination to update or upgrade one's components over the years?

For anyone who is interested, here is one way (my current setup) to obtain 17 or 18 useful non-redundant ratios with a 7-speed freewheel or cassette: 48-40-24 / 13-15-17-19-22-24-26.

On one of the road bikes, here is how I obtained a good 40-to-100-inch touring range with short-cage racing style derailleurs: 48-45-34 / 13-15-17-19-21-23. With this half-step-plus-granny setup, one normally rides in the 45T ring, using the 48 for in-between ratios and the 34 for climbing. Want a wider range? Try 52-48-34 / 14-16-18-21-24-28-32.