Just observed something at SEA today which struck me as curious, and was wondering if the tech/ops community had any insight. I was waiting at the C concourse around 11 am today (2/17), and I saw two planes being deiced at the gate prior to pushback. One was a 739 going to SJD and the other was a 738 going to GEG. The odd thing was both aircraft had come in from other cities, so they weren't RON aircraft. Furthermore, the outside temp was way above freezing (44 deg F according to wunderground), and the cloud deck was low, but no precip since the prev evening. Not that I'm questioning their decision to de-ice, but I just couldn't really figure out why it was needed. Anyone have any insight?