Did you read the article though? They are offering 90 days to make the decision, and a month's severance (miserly, imo, but they're offering it). As mentioned in the piece this wouldn't be a very manageable or predictable way to reduce headcount. It's much more likely the motives are exactly what the company said the motives are: they feel like they will be more effective working together. I would likely be one of the employees who said goodbye rather than move, and I don't think this is ultimately a good decision, but neither do I think it's necessary to dig for hidden motives and agendas.
From my understanding, and this will vary from state to state since unemployment insurance is managed and dealt with by states, not the federal government, employees would still possibly be able to collect unemployment after that month of severance runs out if they are unable to get a new job (and are actively looking) and the unemployment claims will still ding IBM. That month of severance offsets their unemployment insurance rate increase(s). IBM is hoping folks can find a job in the next four months so they don't have to pay any out. Additionally, I would assume, part of accepting the severance might require the employee signing papers which state that the end of employment is voluntary and agreed upon possibly invalidating the employees claim to unemployment and thus hurting IBM's insurance rates. Whether that applies or works will depend on numerous factors, particularly the state the employment occurred in.
The relevant statute is called the WARN Act, Worker Adjustment and Retraining Notification. This requires 60 days notice (or 60 days pay) among other things.
No, in my experience accepting a severance payment does not prevent you from claiming unemployment benefits, however the severance is treated as salary and you can't collect benefits until however many pay periods it represents have passed.
