Although your advice is sensible and is grounded in logic, there are many other variables involved that have a very powerful effect on the final outcome...
Although you say its better to start somewhere down from the very top and work your way up equipment wise, there is a real possibilty that buying something very nice will inspire and even drive you to do more with it.
Another possibility is that the quality/design and execution of top of the line bikes translates to alot of people in reality as top of the line riding experience. I test rode no less than 9 different bikes before settling on the Trek 5200, and not because it was a Trek, but because it was the one bike that felt the best, and believe me, the sticker shock was more than enough to dissuade me.
The decision point was; should I get the much cheaper bike that felt uncomfortable, or the insanely expensive one that felt great!
If a person were to get bike of lesser quality and then quit cycling, there would always be that nagging thought "If the bike had only been a bit better...." as opposed to "cycling just didn't agree with me, and it could NOT have been the equipment I was on, it was the best!"
Isn't there also an issue of resale value or percieved value? If you buy a lesser quality bike, chances are it will be hard to get rid of, or get rid of at a fair price. If you buy a top of the line bike and it had relatively low miles, you would have to beat off all of the ebay buyers with a stick!
I am convinced that, as with all things in life, some people are predisposed to certain activities and turned off by others... Good bike, fair bike, incredible bike, it makes no difference... If the person is not predisposed to cycling, nothing will get them to cycle... The spectrum of quality and cost of the bike will go along way toward fidning that nebulous "edge group" who could fall either way... Having a great ride goes a long way to starting a long and fruitfull pursuit in cycling... and if it doesn't, there are more "escape" routes to recover your loss than if you go the frugal route...
Just my 2 cents
Have a good one!
Feanor