Here's how it works most of the time.
1) Contrary to popular belief, it is perfectly legal to travel domestically on an airplane and carry over $10,000 in cash. You only have to report it when traveling internationally. However, the TSA folks also have the right to question you about why you have that much cash. Technically, they can't detain you but some of them are bullies. There was a particular story of a man traveling from NY to Vegas carrying $6K. He was questioned for a while for carrying such "an extravagant amount of money." Perhaps it's extravagant to a TSA agent, but certainly not for someone going to Vegas. Further, you run into the possibility of a lot of other passengers seeing how much cash you have with you. You want to avoid that.
2) Even if you get into Vegas with cash taped all over your body, you'd never get out with the new security scanners. The new scanners will see they cash on your body.
3) If you bring $10,000 in cash, win $2,000, you can't take all $12K to the cage and ask for a check. You can only get a check for your winnings (so you could get a check for the $2K). This is to prevent money laundering. There are some exceptions to this rule, but it's too shady for me to know anything about.
4) If you are going to bankroll $10K, you don't need to bring it in cash. You can simply wire the money to the cage in advance. In addition to being nice and safe, there is another benefit. You will get noticed by the casino for wiring in that kind of money and I'm sure they will also take care of your room, meals, etc.