Most big projects require a research & planning phase where a small team tries to learn everything possible about the domain, works out exactly what the opportunities are, and runs a few small trials to verify their assumptions. This is not capital intensive, and it's a good time to build up capital & goodwill for the rollout.

I didn't mean to imply that they are waiting. This is just one part of the preperation stage, so to speak. In fact they already have begun. (see the end of the article for links to rumors and actual current movements into logistics by Amazon.) The timing and the incentives (employee retention) line up.