The purpose of EICAR is to provide a cross vendor file that will be detected as a virus. Why? Well, imagine you are building a web application that allows user uploaded content, for example. Into this solution, because you are security-conscious, you might want to scan the uploaded files and remove those files that are malicious before you spread them to other users in your userbase. Many antivirus vendors provide command-line executables and solutions that can do this; what you then need, as a software engineer, is something to test this construction with, either automatically as part of unit/functionality/UI testing or just plain old "did it work" testing.
Enter the EICAR test file - a file all virus vendors have agreed will produce a positive response. As the intended use page puts it:
Using real viruses for testing in the real world is rather like setting fire to the dustbin in your office to see whether the smoke detector is working. Such a test will give meaningful results, but with unappealing, unacceptable risks.
Since it is unacceptable for you to send out real viruses for test or demonstration purposes, you need a file that can safely be passed around and which is obviously non-viral, but which your anti-virus software will react to as if it were a virus.
My understanding is that you do not use the EICAR test file to audit the status of your antivirus products and how up to date they are; you use them to test, in integration scenarios, a case where malware exists without using real, actual malware.