My guess is that they are significantly reducing stock ahead of a fall series 7 release. I don't know this at all, but it wouldn't surprise me if the natural titanium watch is one of the weakest sellers, since: (1) most people choose the cheaper aluminum, and (2) of those who don't, many will choose the blingier SS so that their "upgrade" is more obvious. I like titanium as well, but it doesn't surprise me that it's in short supply right now.
One thing I'm wondering about, though, is whether it sold well enough to be carried forward to the series 7? I hope so.