Hmm, yeah I see where it says that Jeff. I may be wrong here, when I wrote my view (about 2-3 years ago) I was still working on both 2000 & 2005 most days and I remember having accuracy problems that ultimately caused my to add DBCC UpdateUsage periodically. But it may have been only happening on SQL 2000.
Either way, it doesn't hurt to update usage as long as you have the time. The important thing about any of these techniques (yours, mine and Jeff's) are that they are not cursor based and return the desired results.