How dirty your drivetrain gets is a function of where you ride. I've got chains that have lasted two or three years, with very minimal "stretch," riding on the indoor velodrome. I would imagine if you rode in Arizona, things would stay pretty clean with little chain stretch. But ride in the Pac NW or around the Great Lakes, and I would imagine your drivetrain would be clogged with balled-up black dirt and you'd be lucky to get even 2,000 miles (just over 3,000 km) on a chain.
I ride a fixie all the time, and I'll get between 2,000 and 3,000 kilometers out of a wider 1/8" track chain during the winter. But the brake pads are usually the first to go, and rims don't last long either. Last year I went thru at least seven chains and seven or eight sets of front brake blocks, with most of the wear happening in the fall and winter months.
So yes, you do have to do some regular maintenance of your bike if you live in the rain/snow belt. But at least the amount of work you need to do is pretty minimal compared to if you were a cross-country ski racer, having to wax up before each session, removing wax with a heat gun and scraper, structuring the base with a metal edge, hotwaxing, scraping, brushing, etc etc. between sessions, and for each set of skis used. I like just cleaning (wiping down) the chain and lubing every now and then.
PS - you can get a cassette cleaning brush to keep the cogs clean, but the greasy stuff just flies everywhere. Just use a small screwdriver to break up the gunk, then run a rag between the cogs.
Luis