Bro, with my limited experience of playing few online Matches/Tournaments in both PC & PS3 platform, I would definitely say that there is a huge difference between Career Mode and Online play.
1) In career mode, you can predict and guess the bowling (Speed & Type of delivery) correctly about 80% of the time, in online against an human opponent (If he is good player), it is very very hard to predict what he is going to bowl and if you try to predetermine what you want to play, most of the time you will get in trouble. So, you really need to have good reaction time to play a shot according to the ball being bowled.
2) The difference in ball speed (for both Pacers & Spinners) is not very extreme in Offline/Career Mode, but in Online the difference in ball speed is too extreme.
3) In Online matches, good players set field to make scoring runs as difficult as possible. In Offline field placement is quite predictable.
4) Last but not the least, you need to watch out for the d***H**ds bowling Slow bouncers with both Medium Paces and Spinners, which are very difficult to negotiate.