That is true to certain extent...in the US at least.
You can only write off the amount you spend on gambling (the losses) to the extent of the winnings. So, if you won nothing in a calendar year, but spent $1000 in tickets, the amount you can write off is $0. If you won $2500 but spent $1000 on tickets, you can write off the $1000. Thereby reducing your tax obligation to $1500.