Fitness vs image

[LimaDelta]

A few of the guys I work with ride road bikes - fancy carbon framed lightweight things. Very nice and one guy competes regularly so I can see the point there. Others however claim to ride to improve fitness. My argument is that surely dragging around a cast-iron $100 supermarket bike with two flat knobblies and draggy brakes will make you much fitter than some $6000 race machine? If fitness is the end goal why try to make things easier? Am I wrong? Surely the heavy bike will give you the same energy expenditure in much less time and for much less money? Is it simply that they don't wan't to be seen on some cheap POS?

[LimaDelta]

^^^ All seems reasonable enough, but for a car analogy, there is more to learn (and enjoy?) in driving a slow car quickly, than driving a fast car quickly. Maybe the $100 supermarket bike was taking it a bit far, but why not train with a bit more ballast?