What's the difference between bitcoin and dollars?
Bitcoin isn't regulated by any government. It isn't created "out of thin air" as fiat currency is. There will only ever be a finite amount of bitcoin, which controls it's value. Once all bitcoin is mined there will be 21 million in existence, that's it. No one can ever create more (as is done every year with fiat currency). When fiat currency is created by central banks they reduce the value of the existing currency in the market, which results in inflation of prices. This is why the price of every day things (that haven't changed in 50 years, like groceries or utilities) have gone up in price over time. There's a lot of other differences, but it's better for you to read up on them.
And another difference about Bitcoin and Dollar is that while Dollar is the official currency of the United States of America, Bitcoin on the other hand is the official currency of freedom, anonymousity and unlimitability of transaction, which is not controlled by anyone, but whose value controlled by market demand and supply. Whereas the similarities between both is that while Dollar is a currency on its own, Bitcoin is a currency whose current value is measure in Dollar.
Why would I gamble with bitcoin?
I don't, but if you want to you can gamble for significantly smaller portions of money (like cents as opposed to dollars or tens of dollars). And you can do it from the convenience of your computer.
Yes, there is nothing bad with gambling with Bitcoin which happens to be a digital currency, but only with an amount I can always afford to lose at the time of gambling.