Here you find percentages how likely things are (they are always an upper bound - this is why they sum up to >100) but consider - the ones with a (*) are predictions that are right now not backed by someone.
This means until now people are only willing to bet against bitshares.
Lets take the ≈10% for bitshares passing LTC by Sept1.: What it means is that someone is willing to bet on litecoins and is willing to give odds 11. (He bets 10 and someone else could bet 1 against him) The winner would get 11.
Since no one is willing (at the moment to take this odds) the assumption is that the likelihood of this event is <10% (since otherwise probably someone would take the bet)
As soon as someone is willing to bet ON bitshares we can give a upper bound for the other outcome. (Bitshares passing LTC). If you click on "use the advanced form" you see a visualization of the bounds. If you play a little bit with the slider you should get the concept of odds and corresponding percentages.
Information obv. get more reliable with more participants and higher volume. (normally as soon as >100mBTC are bet on both sites the values turns out to be pretty realistic) (since if they are not someone would come in and take the arbitrage opportunity)