The bugs were probably there even during the community day... however, the biggest game-breakers (the autosubs problem, injured players still showing up on the floor, etc.) you won't really be able to see in 3 to 5 minute game with limited hands on time.
What is disturbing is for EA to alot such a small amount of time for hands-on impressions... perhaps they knew even then that with longer play time, more of the bugs would be exposed "pre-maturely" and thus affect their sales... naturally gamers like us won't want to buy something that was broken in the first place. A more prudent action I believe would be for them to have delayed release and fix everything up first before going forth. They didn't have to tell us why... they could just say there were critical gameplay issues that needed ironing out.
What they did now is just an act of pure selfishness and greed... and the general lack of response from them bolsters this impression further... shipping a basketball game where the AI doesn't sub players and teams have 6 starters? They must be playing some other-worldly basketball or something over there in EA Canada...