Intertops proposition bets!

[PO69]

How do they get away with offering bets like these below? I mean they only offer 1 side to the bet and give pretty shitty odds on the side that is offered. Like for instance, in Survivor, they let you pick between everyone left in teh game, EXCEPT the first and secomnd place finishers ROB and AMBER! Check out these other examples


MLB 2004 Special: Any Team to score 25 or more Runs in a Single Game
Closing Date: Apr 06, 2004 19:00 GMT 0

Simply select whether any team will score 25 or more runs in the 2004 MLB regular season.
Pre and postseason games do not count.
All bets are action.
Option Win Odds
YES +300
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MLB 2004 Special: Any Team to record 20 or more Consecutive Wins
Closing Date: Apr 06, 2004 19:00 GMT 0

Simply select whether any team will record 20 or more Consecutive Wins in the 2004 MLB regular season.
Pre and postseason games do not count.
All bets are action.
Option Win Odds
YES +700
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MLB 2004 Special: Any Pitcher to record a Perfect Game
Closing Date: Apr 06, 2004 19:00 GMT 0

Simply select whether any pitcher will record a Perfect Game in the 2004 MLB regular season.
Pre and postseason games do not count.
All bets are action.
Option Win Odds
YES +400
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Survivor All-Stars: Who will survive without Amber & Rob M.?
Closing Date: Apr 02, 2004 01:00 GMT 0
Odds on other castaways available upon request
Option Win Odds
Tom -10000
Jenna L. +350
Rupert +1000
Kathy +2500
Shii Ann +2500
Alicia +3300
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Another example is whether GEORGE BUSH will be the first person on Mars. OF COURSE only yes is inlcuded!

How do they get away with such shit bets?