DWTA actually. It's a motherhood statement to say that there is always change, but it is certainly not true to say that the change that is occuring is always significant, or always at the level that is going to impact on the team.
Take the given example of the Aus teams of 99 cf. 2007, vs 07 cf. 09. What changed between 99 and 07? Steve Waugh retired, and was more or less replaced by Darren Lehmann, then Michael Clarke. Mark Waugh retired and was replaced more or less by Damien Martyn, and then Mike Hussey. Gillespie and Kasprowicz left and were replaced by Clark. Some big names went out, for sure, but very good replacements, so the level of change was not hugely significant - especially as the exceptional individuals who made the team outstanding remained and continued to be remarkably consistent - eg. Warne, McGrath, Ponting, S.Waugh (for most of that time), and Gilchrist (for most of that time). I know I've probably got some of the precise changes wrong, but that's an accurate listing of who substantively replaced people as long term team members.
Compare that to what's happened in the last twenty four months - we've lost Warne, (and McGill and even Hogg) - to be replaced by no-one yet. We've lost Gilchrist to be replaced by Haddin - that's a pretty good replacement, albeit one that took a little while to find his feet and remains to be proven away. We've lost McGrath, to be replaced by Johnson and we've lost Martyn, replaced by Symonds, with a bit of shuffling of the order. Those are two pretty massive losses to the team - as well as Johnson has started to perform. This has meant that once Clark was injured, and Hayden and Lee have had significant form slumps, the core of what was a great team has been almost entirely gone.
There's nothing special about the baggy green that makes "Australia" the best team in the world - its the players on the pitch, and Ponting aside, this summer, none of the players in the team have been the players that were part of that champion team - and even he's been somewhat down on form from his best.
That's not to say we're doomed to years in the basement, or that we're not still a very good team, capable of mixing it with anyone, but we're clearly not the standout number one team anymore.