Really! It does. And I thought that it was just a marketing.
The card was connected to a 1440x900 monitor, and was used happily ever before, without ever thinking to connect to another one. I guess I thought that 1440x900 resolution was enough to fill the ram and even more, not thinking too much of it, but wondering about the 256MB ram sitting idle.
I connected another monitor with 1920x1200 and - it did use more ram (826MB).
So, just me, no conspiracy here