Yes. This is a given. Whoever or whatever came first usually dominates.

Yes. Since Bitcoin is the first, it's normal for it to gain popularity over the other currencies. Popularity brought about by media, community, and even governments.

Yes. Due to the demand and supply ratio which led to Bitcoin's high market capitalization made it the top and dominant digicoin at present. I believe that the only time Bitcoin will be outthroned is when the last Bitcoin has been mined. Now that is still a pretty long time from now.