my theory (spoilers)
Watched this last night for the first time in about 10 years, and I couldn't help but think the entire story (save for the 2 Harvard interviews) takes place in Ben's imagination.
He read Bringing Down The House and concocted a "life experience" story based loosely on that.
I think he's even lying about his lifestyle prior to Vegas - hard to believe that someone with those looks, brains and likeable personality wouldn't be more popular and have a bigger circle of friends and a girlfriend, but by claiming to be an outcast beforehand, it just adds to his nerd-to-cool-guy-transformation story. Also hard to believe Jill Taylor would be single when she's so sought after.
It explains everything else - the fantasy version of Vegas (which is almost as sugary as Richard Curtis' fantasy London), a system which should only give them a 1% advantage paying out such huge dividends every time (and only finally making a small loss when it's needed to push the plot forward), the ill-conceived hiding money in the ceiling, and that convenience of the story being impossible to prove - no money to show for it, no-one in authority at MIT can vouch for it because it was kept secret etc.
In other words, all the flaws or ridiculous moments in the movie can be forgiven because they were part of a nearly 2-hour fantasy sequence.