Working for a dealership myself, I can explain the initial reaction here. Yes, most dealerships will have a general policy to charge a minimum fee (like 0.1 hr, maybe $10-$15) to reset a service light ONLY BUT that's only done to keep everyone and their brothers from stopping in whenever desired for their free service light resets. The fee effectively stops that otherwise we'd be resetting many service lights often for free, taking time away from our paying customers.
Now........although most dealerships do not reset service lights with a LOF ONLY (especially if the service lights also on and a major service is due) by their "rules" and the customer declines the service, some dealership people will still be nice about it and reset the light anyway so as to not upset their customer, ESPECIALLY if the customer has spent money (like yourself) on other work performed.
Getting and keeping good CSI in todays Volvo dealer is a big deal these days and to us (where I'm at), it's simply not worth upsetting a paying customer by leaving the service light on knowing that that will be something that'll upset him/her so we'll usually just reset it. Now, if you just drove in and were not a customer (no service history ever), then we'd charge you to reset the light only.