From what I remember, the SP2 CDs took a while to appear for order, and probably the same will be true of SP3 ones.
They might not even do it, because nowadays, dare I say, most people either have broadband, OR know someone with it, so downloading the ISO image or the Network install isn't as much of a problem as it used to be. But maybe that's me being too blinkered? Dunno!
Even the
Windows XP Downloads page doesn't have SP3 listed anywhere! Looks like it really was just quietly rolled out, and the site stuff comes later.
SP3 isn't anywhere near as big a change as SP2 was, so there isn't the great push to install it like with SP2, so perhaps they're being a bit more laid back about the whole affair. Plus with M$ trying to push us all onto Vista, they may be less likely to make it easier for people to stay on XP?
Will be interesting anyway, to see what develops