I'm going to cut and paste my rant from the other thread, since it applies here also.
Here's the reason. I can halfway trust his phone polls, because I'm sure he conducts phone polls like everyone else.
His internet polls derive from a self-selected group. It is essentially those people who sign up for his polls on the Internet. We can see the people this type of method will tend to favor and the type of people it won't. His survey is full of those people who are super-interested in politics (typically partisans) and have Internet access and who also know who in the hell John Zogby is. People it would leave out are those who not figured in this list.
I am actually one of those people who took this poll. Not that I care about the results, mind you, but as you can see I fit the description perfectly.
