Why avoid weights?

For what it may be worth, I avoid weights because I want something I can do every day, any time, anywhere. Because I know that if I miss one day, there's a good chance I will fizzle out.

So I do pushups, crunches, and pullups. I have a pullup bar at work which fits into the door frame and the same thing at home. But sometimes I do pullups on the subway or on one of the many scaffoldings in NYC.

Using weights might very well be superior in some respects but for me the main thing is consistency.