You can indeed
Depends on what you class as average. Most road bikies that ride a lot buy a lightweight road bike with 10speed gearing. ( Apart from Brett who rides a fixed and thats just an age thing).
If your doing lots of miles then your average bike becomes hard work. Weight, tyres and other things become issues.
Ive converted many a cyclist who has been struggling with a heavy bike with knobbly tyres on and have just about given up. They have a little go on my road bike and think God its a lot easier. In reality its not easy but for your general average cyclist who just wants to do a few miles at a steady pace it is.
You can now purchase a lightweight good quality roadbike fairly cheap.