Hairspring, is still largely made of metal ( except few silicon based ones), however light it might be is still subject to gravitational pull , so if left sitting idle for extended period of time, it can be VERY slightly pulled out of shape and affect accuracy .
While modern synthetic lubricant is much less prone to drying up during long time storage, but it can still concentrate and run out of place during storage and as a result, increase wear and tear, again, it's due to gravity and the nature of , well, a liquid.
So it's still a good idea to keep your pieces running for at least a day every month.
As for boutiques , they usually have a policy to wind up the pieces every few weeks.