@Lheann: Something seems to be off with your numbers there. My fully updated live client is 3.04GB, Testlive is 3.05GB
Maybe you have the testlive client on a subdirectory of the main AO client? That'd make up for the 6GB you're experiencing.
I'd assume the 23.8GB are not from this engine, therefore not indicative of 18.7 itself.
To the topic - Yes, the requirements are very, very outdated. Though changing it now to something including "DX7 compatible graphics card" instead of waiting for the new engine to come out and take that opportunity to upgrade the specs to more modern standards would likely be a worse choice for FC's marketing dept.
That said I'm 100% for practicality over marketing so.. update the damned thing! It's a 2 minutes fix.