As with a lot of hiring questions, "it depends". The human element in hiring can't be ignored.
That being said, there are a couple of things to keep in mind.
Are you going to be talking to a big company or a small one? Bigger companies might have HR personnel who aren't necessarily game developers who do the initial filtering. They might be more inclined to look at appearances for their opinions on candidates than, say, the art director at a small company simply because they don't have the expertise to really look analytically at someone's portfolio.
Also, remember just like any other job you're going to be working side by side with people for (hopefully) a long period of time. First impressions matter. As an interviewer I'm looking for both game development skills and people skills. Namely, am I going to want to work side-by-side with whoever I'm talking to? Do they show poor judgement (like wearing an offensive t-shirt to a professional setting where they don't know the audience)? How's their hygiene? Dressing sharper might help with those sides of things.
But don't dress sharp if you don't know how. Don't wear a button down shirt that isn't ironed. Don't put on too much cologne. And if you're not comfortable in a tie, don't wear one. An interview is stressful enough as it is, and you don't want your clothes working against you.
I've interviewed junior candidates that wore suits and ties. If we thought they were smart (and likely to get the job), we'd poke fun at them a bit. Mainly just to get the point across that our culture didn't really care about that kind of thing (and, as far as I know, most game companies really don't care). But generally it didn't count against them.