Reply to myself:

> Anyone has an idea why it will come with only half the amount of RAM that
> the X1000 product page claims [...]?

Trevor Dickinson answered this one in his AmiWest 2011 presentation:

"This is the base system. We're trying to keep the price down for you guys. We're trying to keep the price down for the minimum. [...] So we're putting in 1 GB RAM [...]. We wouldn't recommend that minimum. I'd go for 2 [...]"