Define "logical internal structure"? Most code in a library won't be differentiated by use unless you can provide WPO or PGO-based feedback that you trust as representative. As for the next obvious question ("why not just read in the whole thing?"), I think you can probably guess.

I'm not sure how yucky this is. The world is analog. MSFT made things go faster without asking developers to change anything they were doing. I wish more OSes showed more of this sort of user-centric, data-driven prioritization of feature development.