Why would 8 mil US citizens make this up ? i'm sure there are many frauds and maybe one with sleep paralysis, plus the military abduction stuff.. but what about he 7 million others? they aren't all selling a book. are they?

The correct number is 3.7 million, which resulted from a Roper Poll conduct in 1991-1992. Bud Hopkins was among those asking the Roper Organization to pose questions in this area. Around 6,000 persons were questioned. However, they were not asked "were you abducted", but rather 5 questions, and Bud Hopkins then concudes that if they answer "yes" to 4 of them, it is an indication that they were "abducted" by aliens. The poll is flawed.
See

http://www.csicop.org/si/9805/abduction.html