Because the media was so careful to seperate the fact that companies like Enron and Worldcom were running rampant in the 1990s while the Clinton admin was taking responsibility for the invention of the internet and all of the wealth (albeit largely temporary) it created. And, the MSM was very careful to point out that the recession that we probably weren't in at the beginning of the Bush administration started, if it existed at all, before Bush was even in office.
The fact is, Gross is wrong. Obama could have a great effect on the economic health of the country, but he won't. He'll choose, instead, to buy votes by inflating the currency even further. Of course, McCain will do the same. So, vote for whomever is better looking to you.