It's not clear from the original article... is this an internal helpdesk or a customer-facing helpdesk? If you're in a customer-facing position I agree that a look that reinforces your "brand" is good business. If your "customers" are all internal, though, then I have to wonder about management's motivations. Either they're trying to send a subtle message about your current mode of dress, or else they're scheming to get more attention (and resources) from upper management ("We want to make sure they KNOW who helped them out come budget time!")

A more-flexible and less-costly alternative to shirts, though, might be special "help-desk" *badges* that you wear when you're on the clock. These serve the same branding function, but you only have to buy one per employee (if they expect you to wear the shirts four days a week, they damned well better issue at least four shirts per employee!)