Can a distro really hope to do much more than this apt-get one-liner can?

Yeah, you could install an improved collection of prewired config files for everything so that all the tools are better integrated out of the box. But given that each web 2.0 app probably has a unique configuration, which requires a sysadmin to hand-edit all of those config files anyway, is it really going to save that much time? Configuration space is kind of large. The odds that the prewired configuration is a close match to the one you want may be fairly low.

And if your code doesn't need a custom configuration of servers, but is designed to run on some kind of standard server-farm-in-a-box configuration (with, at most, minor tweaks of a couple of config files), why are you even installing your own distros? Aren't there hosting companies that run farms of standardized boxes that your app can be designed to, and that will handle the provision and administration of those boxes for a monthly fee? Kind of like the Google App Engine business model? I haven't done business with such a company, but I've been presuming they exist. Isn't this how (e.g.) Engine Yard works?

The potential problem with the distro idea is that it sits between these two business models (bespoke setups by your own sysadmin on the one hand, one-stop shopping for standardized architectures, standardized server farms, and standardized sysadmins on the other). Is there much daylight between the two?