It turns out that all this time Apple themselves have had a better collection of their specifications at http://support.apple.com/specs/.
So, for example, I find that my dual G5 had:
Or, in more detail:
"Optical drive bay with SuperDrive (DVD-R/CD-RW) installed; writes DVD-R discs at up to 8x speed, reads DVDs at up to 10x speed, writes CD-R discs at up to 24x speed, writes CD-RW discs at up to 10x speed, reads CDs at up to 32x speed.
Finally, the build-to-order options were:
SuperDrive (DVD-R/CD-RW), Combo drive (DVD-ROM/CD-RW)
This contrasts with lowendmac's rather useless "8x SuperDrive standard on all models". I suggested to them a few months ago that they could usefully be a little more specific, but received a reply that made me wonder if they even spoke English.
Obviously, if you're on the console, you can ask System Profiler exactly what's fitted, and even find the manufacturer, model number, and firmware version. But sometimes you're not at the console, or you want to know what someone else's computer might have, or you're trying to remember what an old machine you no longer own had. Sometimes, as yesterday, you want to answer a question that the computer itself is unlikely to help with, such as "how heavy was my iPod?".
"apple specs" appears to be the most convenient Google string. I don't know why I've never come across it before. I'll have to remember to use Apple instead of "lowendmac" in future.