This has nothing to do with the 'loose pages' that some countries will offer for immigration stamps (ie. TRNC, Cuba, etc). Those may be given upon entrance to another country, for the convenience of avoiding permanent stamps.
If you're getting a new passport you can get the larger book in advance, at the same price (see the original article, which gives the same information).
If you're overseas and your passport is very close to full, the local US Embassy may extend your passport if needed. I say may as I'm not speaking for the US govt, and my understanding & personal experience was that they only liked to do that for expats, not for tourists. Note that getting the additional pages sewn in, while official, also seems to correspond to additional hassles at passport control (US & other). If your passport is close to expiring, getting a new one with 52 pages may be easier than getting additional pages inserted.