Yes, but I really doubt it's still a supply issue anymore. A month ago I would agree, but it's been 65 days now, the new Mac Pro shipments have slowed by now, and so the only thing that there is a possible worry about is having enough for when they make it available.
Another thing is that you would think it would be made available, but with a shipping estimate of a few weeks or something. The fact that they aren't doing that means they are not sure the exact day they are going to start shipping them. If it is supply, then they are waiting for the lead time to get shorter, and so they wouldn't know when that would be exactly.
So it could be supply, but you have to think it would be resolved by now. Somewhere there is a warehouse full of 5870s that are actively being put into custom Mac Pros, but they can't start selling the upgrade kits yet. It's just odd.
Depends entire on how much attention Apple is paying to shipping these things.
There was a report that someone called ATI a few weeks ago, and ATI indicated it was still a supply issue, and that the supply wasn't scheduled to be ramped up until later. I think it was possibly this week the supply was to be ramped up.