Nothing wrong with riding on a cheap bike of course, but your latter statement doesn't really ring true to me.
The "extra" money into more expensive bikes may partially be marketing/name brand but most of it either goes into making things lighter or stronger (and sometimes both). A real touring spec bike will tend to be on the heavier side (at least, compared to race bikes) but be much stronger than a typical bike. They really are pretty robust. I don't know if your friends were just unlucky and you were lucky, but it might just be sample size, as you'd really want to measure this over much longer times/distances.
I have friends who pretty much always ride cheap bikes due to losing them semi-regularly in the city. The main differences between them and more medium-price bikes seem to be: poor brakes and clunky shifters, and occasional catastrophic failure of components (i.e. not repairable without replacement). Oh, and they tend to be heavy.