I know it's not the slightest bit important. And he's not drawn anatomically correct or anything. I know that folks always joke about how stupid it was that Donald Duck cartoons were banned once because he didn't wear pants. And it's no different than other cartoon characters. Looney Tunes character designs rarely include clothing for example, as long as they're not wearing skin-tight black spandex and flying through the universe with lazer-vision fighting crime and pirate ninjas and shooting up crack BECAUSE IT'S EXTREEEEEME!!! But I digress.
Just another example of me thinking too much, I suppose. But it's still pretty damn weird since we've been used to seeing Sonny with clothes for so many years. I mean, even though Bugs and Daffy are usually sans clothes, wouldn't it be weird if suddenly Mickey Mouse never wore pants again? (Pervert...)