Have tickets ever included free GO? That's the first time I've heard of that, and I've been a long time Blue Jays fan.
Not for Blue Jays, but I have heard some events (e.g. concerts) turn your concert tickets into a free GO ride the same day. A concert last year made your concert ticket a free GO fare, and Metrolinx tweeted it too. And for other upcoming events such as PanAm/ParaPanAm Games.
I presume Metrolinx gives a discount fixed rate to the event organizers (maybe $1 or $2 per event ticket), as a transit advertising opportunity, as not every single attendee would take GO anyway. Maybe Metrolinx does this for free sometimes as a quid pro quo from time to time (as GO advertising cost, while event organizers have a promotion opportunity) -- or as a test case, to see how it affects adoption. Either way, it seems to be a tactic that's happening for several events nowadays.
Also PanAm games this year -- if you have a PanAm ticket to any event, all your rapid transit and commuter rides GTA-wide (GO, TTC, MiWay, etc) are free for the whole day of the ticket. Have my tix to the Cirque du Soliel opening ceremony and gold medal soccer game (soccer playing 1km from my home in Hamilton, but will take GO to the opening ceremony). Although the Games itself are somewhat controversial, I love the idea that my PanAm ticket gives me free fare all day long on both GO and TTC -- and it might even pay off by attending one the cheaper PanAm events (e.g. boonie bleachers for a minor event, and/or support the disabled athletes of a ParaPanAm game) just to take advantage of free GTA-wide transit rides in both directions, and also enjoy being in Toronto for other reasons.
All the free transit rides for one day, can actually cost more than some of the cheaper PanAm tickets! The event ticket printout is all you need to show the fare inspector, and hopefully even introduces a few new car users to GO, etc.
It's a great idea, really -- reduce car traffic to downtown during major events.