I got my 11" MBA Saturday at the Mall of America Apple Store. I asked them if they had any models other than the 4 standard. The guy said no. I had thought about upgrading it here and there, even though I felt I didn't need it. I only used 28 GB of hdd on my old MacBook. On my MBA, iStat has just barely gone over active/inactive ram. So, I'm quite sure the $999 model will serve me well.
The big thing for me is I really wish it had a newer processor. I thought about waiting until they could fit a Core iN and fancy graphics. Problem is that could be 2 years. I will stick with my $999 MBA and maybe upgrade in a year or 2 if they come out with something drastically better.
Which they of course will....