I do not mind if people use common abbreviations, since they usually really help to speed up a typed conversation (which is a good deal slower than a spoken one).
Additionally, I can understand if somebody "plays around" with the language (e.g. by purposefully mispelling words or replaces letters with numbers) in an email to a friend. However, the internet being what it is, such jokes sometimes get out of control and survive long beyond their best-before-date. By now it 1337 is neither funny, nor new, nor original, it just smells badly and spams up conversation. For somebody like me (not being a native english speaker) 1337-speech makes it really rather hard to understand the sentences. 1337-speech, being just badly mistreated english without offering any benefits (such as faster typing or faster reading), thus has (imo) no right to exist anymore (other than to use it now and again to make fun of immature teens who still think, 1337 is cool).
In a fantasy-game an overextended internet-joke should not be allowed to appear.
P.S.: Of course, being a german, I also tend to mistreat the english-language now and again...