The $30 number comes from the original article -- If I were to make the colo data transfer free and change nothing else, break even point is 100TB/mo.

For the employee cost I agree if you just have a couple boxes pumping out data your labor cost will be quite low. I'm imagining what else you might have happening on your back end using AWS services that you'd also have to replicate in your colocated installation to preserve the efficiency, which would take labor. For example, if you want some extra machines to do some load testing. Or if you need to store a bunch of data and want an S3-like system. Or if you want to wipe a machine and reinstall from an "image". The backup system, and backups testing. RDS, Aurora, DynamoDB, etc. Most of that can be done with a couple clicks on AWS.