I didn't say 100x "slower" but rather 100x complex. I'm talking at the system-call level. The number of system calls required to process an image request that's scripted (especially if it comes out of a database) involves at least 100x more system calls (complexity) than an optimized request using the properly tuned apache module. I saw a big write up on this somewhere, and I can't find it now, but there's a method available in apache that's similar to the scatter-gather I/O used by the
TUX in-kernel webserver. But even ignoring that special I/O mode, a static request is still WAY less complex than a scripted one, by several orders of magnitude.
Now, as I (and you) said, it's usually negligible on modern computers (when you're not serving something like eBay anyway.) But the perfectionist in me hates to see anything wasted. I also see it as an analogy with a race car and a drive to work. Would you rather commute 1 mile to work, or 20 miles across town? Sure, that used to matter... but new computers are like 500mph cars. What's an extra few seconds or so on the way to work? The catch however, is that that longer route, even though the time difference is very low, is still 20x more complex... what that means is that you have 20 times the chance of running into a traffic jam, or having an accident. In computers this amounts to the fact that very rarely are all parts of a system tuned equally. Usually a bottleneck occurs at a specific point (like the database server) and everything else slows to the speed that runs at. The less things involved in a system, the less chance for things to go wrong, or to get hung up by some "traffic jam."
Okay, this turned into more of a philosophical stance/discussion than an actual answer, and I realize I always end up doing this to Data when he posts something about design/sysadmin stuff. :-) I don't mean to argue or anything, I just have a different opinion, and want to elaborate my PoV. I don't do it to prove that I'm "right" or anyone else is wrong, so I hope no one takes it that way. For all practical, sane-scale stuff, whatever works best for you is infinitely better than "optimizing" for the machine.