I've stayed out of this so far because I'm not sure I understand the question being asked. Not that I've ever been stopped by that before, but I'm trying hard to change.
If the flights in question are the dual instruction 100nm day VFR & 100nm night VFR x-country flights, Midlife's answer that "Because the regs say so." is correct.
The reason the regs say so is because these are supposed to be instuctional flights covering the Areas of Operation listed in 61.127 (b)(1). Granted, you do most of those things listed on any x-country flight (or should), but these particular flights are part of the 20 hours of dual instruction required for the rating.