I see what you mean. You're right. The inner two tip and ring wires are used in POTS for a single (first) line.

some wiring links I found
wiring references:
http://yoda.uvi.edu/InfoTech/rj45.htm
http://ckp.made-it.com/twistedpair.html

rj11 and 45 differences:
http://alamo.satlug.org/pipermail/satlug/2003-June/009888.html

on flat vs twisted for data connection:
http://yarchive.net/phone/twisted_pair.html