Employers Forgetting to Remove Access for Ex-Employees?

This devilish Anonymous Coward asks: "Quite by accident, I misdialed the other day and wound up in the voicemail system of my ex-employer, late of some 4 months now. Curious to see what would happen, I punched in my password, and lo-and-behold, I still had access to voicemail. Curious, I checked to see what I still had access to, and discovered that my shell account, Web logins and even the root password still existed as they did when I worked there. While I would never dream of trying anything funny (since they could pretty obviously track it back to me), I'm wondering how prevalent this lax attitude is in today's workplace, particularly in Silicon Valley where employees skip from job to job like mad. I'd bet that way too many Slashdotters still have access to things months or years after they left employment... including some pretty secure things." It's all a matter of the communication channels between the IT Department and Management. Better communication channels means less chance of this sort of security hole happening...or does it?