hmmmm...there are hundreds of bar codes on older games, music, boks etc. under those spine cards if you poke around a lot. i have a couple of old film soundtracks and other japanese lps and a few books that came wrapped as well. also, not all pc-engine games had spine cards- many hucards were spineless, and you'll also see saturn and ps imports that come in some boxed sets are missing them as well. the key is more likely historical (pause for slight comic relief)

...i've heard/read it's possibly a cultural thing. look at all the well-wrapped things in japanese history. a good kimomo, freshly made sushi, the head of one of your enemies in a box full of salt (movie reference). why, spine cards are like sealing wax- you don't need to have 'em, but it makes whatever you're opening so much more special, no?