Obviously downsizing - everything else is flannel.
Whatever they say, the real reason is to reduce their number of staff. Everything else is flannel. 'Move or leave' is the real message, and the subsequent reduction in staff won't cost them a cent... except in good staff, reputation and employee satisfaction. The people they retain will be the dregs who can't get jobs elsewhere, and also will be disgruntled about being forced to move or have long commutes. Let's hope IBM have some good people outsourced already, otherwise IBM will stand for 'I've Been Mugged' if you happen to be a customer.