The answer is simple, said former Denver City Councilwoman Susan Barnes-Gelt: "It's always about access."

It is not a phenomenon unique to the Democrats or Denver. A slew of corporate donors have lined up for the Republican National Convention in Minneapolis, and 20 of them also are sponsoring the DNC.

They include companies like 3M, Allstate, AstraZeneca, AT&T, Burlington Northern Santa Fe Railway Co., Ford, Merck, Qwest, the Service Employees International Union, US Bank, Visa and Xcel Energy.

"Welcome to the American political system," Barnes-Gelt said of the companies ponying up money on both sides of the aisle.

Chris Lopez of the Democratic National Convention Host Committee acknowledged that sponsors get "opportunities" that depend on the level of their support. Those opportunities can include tickets to events surrounding the convention and even access to the Pepsi Center itself, where the convention will be held.

The host committee does not have to file documents outlining the level of sponsorships until after the convention. But Lopez said the access goes up as the contributions do.