One of the things about working in a bike shop is that you have to perpetuate the myth of need. People need a different bike for every type of riding (mountain, road, racing, recreation, mixed-terrain, cross, commuting, cruising to the coffee shop, going to the grocery store, etc., etc.). Obviously, if you have the room and can afford the bikes, having bikes optimized for each activity is nice. I fall into that behavior: I have dedicated commuters, and I have the XO-2 for just knocking around on (or for knocking out a hundred miles in a day, occasionally). But, my "road bike" and my "mountain bike" are the same bike, with a change of tires.
Still, when you are selling bikes and accessories for a living, the more you can push the concept of specialization, both in bikes and equipment, the better. It wasn't always that way, however. Many people my age, and certainly most people who are significantly older, can count the number of bikes they owned through the years on one hand, with fingers left over.
My friend Don, who recently turned 78, owns a load of bicycles, now. He has become something of a rider/collector, since he gave up motor vehicles 15 years ago, and he enjoys finding old bikes and refurbishing them. But, when he was young, things were different.
Unlike some people who will decline mountain bike riding with me because their tires aren't suited for the trail I am planning on riding, Don made do with what he had, and rode everwhere he wanted to go, as a kid.
He told me about his first bike, one day, as we were talking about some of the bikes I own. I told him about my circa 1910 Iver Johnson, and he said, "My first bike was an Iver Johson."
"It had a big, wide, handlebar on it, and fenders. But, it didn't have any tires. So, I took some rope, and cut it to fit arond the rim, then spliced it together. I rode all over on that bike..."
Then, he proceeded to tell me about riding up in the foothills, up north and down south of Denver, itself, on everything from cobblestones, to brick streets to dirt roads. All of this was done with rope "tires".
So, the next time you feel like you can't explore a dirt road on your road bike, or you think that a road ride is undoable on your knobbies, just ask yourself where you would ride if you had rope on the rims!