People don't understand them. The crap coming out against Nate Silver is mostly just people trying to change the narrative, but there is some element of it (and probably a large fraction among those who believe it) that is just not understanding what polling is or how statistics work.
A 76% (or, now an 86%) chance for an Obama victory actually indicates a pretty close election, not a landslide or a sure thing by any stretch. If Obama had a 5% lead nationally his odds of winning would likely be well over 95% at this close date. One day away and less than 90% indicates, to me, that the race is very close. Just because the safer bet is with Obama doesn't mean it's not still a gamble.