Only 5,000 pages? I have books that are over 2,600 pages that don't even break 2.5" (eg Machinery's Handbook). Even using standard 20lb printer paper, my calculations don't have it breaking a foot. They must have used something like card stock, just to add shock value to it.

Seriously though, turning Wikipedia into dead tree media is something that should be taken more seriously. Without much effort, relatively interesting primers on subjects could be put together with relatively little effort. Think "Cryptographic algorithms" or "Battles of WW2" or "Countries of Africa" Collect and curate a selection carefully, and throw it up on some place like lulu.