The Rand Poll surveys the same group of people over and over, with one seventh of them surveyed each day on the same day of each week. The poll results reported today show the first effects of polling done after the last debate, meaning that one seventh of the respondents were surveyed yesterday, the first day after the debate.
Romney's numbers went down from 46.36% to 45.34%, more than 1%, which looks to be the second largest one day drop the survey has ever shown for him, and the survey started on 7-11. Remember, this is the result of only one seventh of the respondents having given a new response after the debate.
Obama's numbers went up from 48.26% to 49.19%, almost a full percentage point, which after a cursory look seems to be the third or fourth highest one day jump for Obama since the survey started on 7-11.
.....because it is an apples to apples view, which more accurately shows the effects of ongoing events during the election cycle. Using a more random method, you cannot really tell how much of a poll's changing results is due to the effects of events or due to the effects of different people being surveyed.