You're reading it wrong.
they gave the ps3/xbox360 a -75%
they gave pc a -85% (for obvious reasons)
I don't think mod-ability should come into play in a review, to be honest.
I also think it was hypocritical to ignore the bugs in Fallout 3 when they reviewed it, but be so picky about it now.
Some people say that NV is way buggier than F3. This has not been my experience. People may forget how buggy F3 was on release. Still, on 360, I find that F3 is buggier now than NV is now. Hopefully, patches for all, but especially PC users with hardware issues, will be on the way.
So really, I don't think the review is rigged- it should have been changed.