Why is cron being deprecated?
With the release of Mac OS 10.4, launchd was chosen to supersede cron in Mac OS. Here's a cached version of the launchd page from the Apple Developer Connection in 2005. It explains why cron was deprecated, as well as the benefits of launchd from Apple's perspective.

The summary: launchd was created to not just replace cron but also init, xinetd for better performance, and better control over configuration and the actual tasks themselves.


  The launchd daemon offers a single, standardized, interface to any and all programs started automatically by the system. Furthermore, the configuration files that determine when to run a given program can also specify resource limits and environment variables, which simplifies setup and security for many programs. The same configuration file format is used whether a job is launched once at system startup or user login, on demand over the network, or at intervals.