I remember very well when the steam has started to receive payments in bitcoin and saying the truth it didn't affected the market.
Because gamers who are bitcoin addicted are not much and the needs for this wasn't too high, we can see that other companies like steam have accepted bitcoin and never affected the market.
I do believe the only market it may affect is the lending service as some people do lend bitcoins taking steam as colateral, besides that some users are ofering those as colateral, something in the past werent possible. In the end it wont affect really the steam accounts market at all, as bitcoin is the same as fiat, soo buying with it or fiat is the same.