What's wrong with that? About a week, which at some point needs to be folded into year-to-year comparisons. Right now, this is no big deal. But things get screwy once the low-rated holidays kick in for measuring how shows performed compared to the same week last year. In other words: Come Thanksgiving, ratings are no longer cranberry-to-cranberry.
More to the point for networks: The early season story is sunnier for ABC under Nielsen's current measurement intentions (so they're wholly in favor of the plan), but would benefit Fox's seasonal comparisons if the extra week is added in now (so they're disgruntled). CBS is cheering on the Fox camp, while NBC's ratings department -- especially after the whole "Heroes" CumeGate scandal- is basically willing to just go along with whatever.
Adding to the fun: PBS drew fire last week for reporting their ratings for "The War" as 18.7 million people that tuned in at some point (a rarely used measurement) rather than the more accurate measurement of 7.3 million average total viewers who actually watched (the standard measurement).
Though this was considered as a nefarious move that, like with "Heroes," derailed a network's good-news story, let's give PBS the benefit of the doubt. It could have been an over-eager misstep rather than nefarious manipulation. After all, how much experience does PBS have in bragging about their ratings?