I believe so.
Due to the fact that the people we meet on the internet are likely a large distance away and will usually never have any contact with our real-world peers, we're more honest with them. It's simply the truth. I'm sure several players reading this post can agree that they are more honest with their online friends. They may not consciously think about their friend not being able to permanently ruin the real-world reputation, but it's subconsciously residing in the back of their minds at all times.
Another factor may be the fact that there's hundreds of thousands of communities online. If anything goes wrong in one community, said user can simply hop on another one. The internet is a great place, and one of the things that makes it a great place is the ability to completely make yourself disappear, and resurrect as an entirely "different" person.
Take
Harmonicat (Arena) for example - he ban evaded on the forums for a significant time before admitting to his true identity.
As for competitive trash talk, and we've all seen it (eZ, rekt, etc), I believe the primary reason is the fact that it isn't immediately apparent that you're talking to an actual human being with a life of their own and very, VERY delicate emotions. When you trash-talk someone in-game, you think no more of it minutes after. However, if you get into a verbal argument in the real world, it's much more memorable and life-changing. Keep in mind that you can't immediately escape drama IRL, which makes being a mean person online much easier.
People do indeed use the internet to make themselves look good as well. I won't call names or point fingers, but there are members in this community that attempt to hold a very distinct image. This happens for the same reason it happens in the real world - to be unique. To stand out. To give people a reason to befriend you. The popular clique online is like the popular clique in real life.
but in real life I have no hope...:/
