The dress code has evolved from dressy-ish to more casual, to appeal to more people.
Regarding the t-shirt that was asked about - it's the style of the shirt. So, while there may be "rips" in it, it's deliberate and not the end result of a bad run in with a pair of scissors.
What we don't want to see is someone showing up in some ratty old t-shirt, ripped jeans because they didn't care enough to clean up a bit. You are going out to a social event.. try a little.
That being said... I am a big fan of nice jeans and a nice shirt (and that can be a t-shirt). If it looks like you tried, odds are you are fine. But if it looks like you just came from the gym.. probably not.
But, like Rathany said, if you have concerns, you can always email kumoricat@ and we will try and answer your questions.