Using shortcuts on a forum is unnecesary, but it is very usefull on live chats and a must in online games. Being killed while typing -thank you- can be anoyng, so it is logical that people write -ty- instead. If you play online games a lot, using them will become a habbit.

As for gramar, you should bear in mind that not everyone is American or English, so right gramar isn't natural to everyone.