No word was given as to why the code, part of the mobile device management (MDM) APIs implemented in last June's iOS 4.0 release, was deep-sixed. The MDM code would, in effect, periodically ask iOS if it had been compromised (i.e. jailbroken). If it had, iOS could then, say, send out alerts to corporate help desks or sever access to Outlook servers.
In addition to Apple's continous "you'll void your warranty!" finger-waggings, the vast majority of businesses that support iPhones and iPads for their workforce frown on jailbreaking, as the exploits used routinely clobber iOS security features.
It's theorized that the jailbreak-detection code was dropped because either (a) it was too hard to implement or (b) many companies had their own external processes to spot pwnage.