Why would anyone, barring a speech impediment, pronounce twat as "twot"?
Would they also say "the cot sot on the mot"?
Did they get the joke in the name of the internet café in GTAIV, or did they think Tw@ was pronounced "twot" as well?
Speaking of the internet, is their e-mail address "I_cont_soy_vawels_praperly ot hatmail dat cam"?
I think twat and twot are two completely different things. Twat is a slang word for vagina and, as somebody pointed out, twot means Total Waste Of Time.
This phenomenon could be an example of people learning their vocabulary, grammar and pronunciation by hearing words (mainly from films and TV) rather than by reading them, subsequently getting them wrong when writing them down, probably due to mishearing the original word.
As an example, I've seen people write "ladder" instead of "latter", as in "Do you think this game sold badly because of poor reviews or because it wasn't advertised enough? Personally I think it's the ladder".