The twitter bot uses the same algorithm for choosing the main tag as the website does when deciding what tag to stick at the start of the question: pick the one with the most question count. If that tag is pc instead of deus-ex-human-revolution, it's too bad.
As such this post is kind of a duplicate of other, simpler suggestions for affecting how the main tag is picked, such as this one.this one. I'm afraid this is a bit too complex and site-specific to be adopted, but obviously it's the team who has the last word .