Or, rather, historical events drove certain solutions, but I didn’t feel that it all was being driven by foundationally sound thinking. GTD rulez, of course, but …

I think the scaling problems Twitter encountered could (/could/ … plausibly) be looked at as a case for this.
For my money the server’s being called too often … I can’t say the downloaded page is too thick, though it’s surprisingly heavy.

Without data to go by, what’s harder to handle: a request for a lot of code? or multiple requests for bits and pieces?

TW is as thick as I’ve seen. In it’s way it’s pure / paradigmatic.