Andy Kroll at Mother Jones identifies 3 main differences
1. Different organizers: In Wisconsin, "the day after Republicans reclaimed the state Legislature and the governor's mansion, union leaders began plotting how to respond to the looming assault on organized labor.... From their command center in Madison's only unionized hotel, labor turned out more than a 100,000 supporters in a span of weeks." But the Occupy Wall Street protesters were responded to a prompt from Adbusters magazine and then grew "almost entirely without institutional support, an organic groundswell without leaders or executive boards or much structure at all."
2. Different goals: The Wisconsin protests, at their height, were focused on something quite specific: defeating Gov. Walker's budget reform bill. "Occupy Wall Street so far has had no clear set of demands—and intentionally so, it seems."
3. Different reaction from the police: Here in Madison, the police mostly accommodated the huge crowds that besieged the state Capitol. In NYC, the cops have cracked down.
Kroll also lists 2 similarities. Both sets of protesters: 1. used social media, and 2. ate pizza.
ADDED: As for that seemingly intentional lack of demands... I think of this: