Scenario 1: President George W. Bush delivers a speech and two audience members are removed because they came to the event in a car with an anti-Bush bumper sticker. Scenario 2: The Obama White House organizes a rally to celebrate Democratic victories in the 2010 congressional elections and a "tea party" member wearing a "GOP" T-shirt is excluded.
The first event actually occurred; the second is obviously hypothetical. But that's not the important difference between the two situations. Nor is the identity of the president.
The crucial distinction is that one is a political rally to which the president and his staff have invited only supporters, as they have the right to do, and the other is a town meeting that was advertised as open to the public. That's the distinction that a federal appeals court ignored in ruling against Leslie Weise and Alex Young in January and that the U.S. Supreme Court should acknowledge by reviewing the case.
In 2005, Weise and Young obtained tickets for a Bush town hall meeting on Social Security held at an air and space museum in Denver. But they were ordered to leave because a bumper sticker on Weise's car read "No More Blood for Oil," a not particularly subtle dig at Bush's Iraq policy. Weise and Young subsequently sued Michael Casper, who ordered them to leave at the behest of White House aides.