I think what most people observe as "raining" is when the ground is wet and the sky is overbearingly gray, looking like it will rain. From indoors, it's quite hard to determine if it is actually raining, and to most people there isn't much difference. The lack of sun and wet ground is more bothersome than precipitation.

If it rains 50% of days, that means the ground is almost always wet, and the sky is almost always dark and cloudy. To most people, that is rainy weather. Furthermore, the air is often misty and wet, but would not be measurable precipitation.

I'd love to see a similar analysis of sunshine. I did find on most days in the Seattle winter, the sun would peak through for a few hours, though usually too low in the sky to promote much Vitamin D production.

Seattle has amazing natural beauty, and sometimes the weather can be excellent even in the winter. Summers are flawless. However arguing that it doesn't "rain all the time" in the winter in Seattle might depend on whether your definition of raining is as meteorologist, or on whether you have to wear waterproof shoes and carry an umbrella.