Risk is more expensive when you have a smaller bankroll. Many slot machines actually offer positive expected value payouts - they make their return on people plowing their winnings back in until they go broke.
Citation please? A cursory search suggests that machines go through +EV phases, just like blackjack, but that individual machines are -EV. It's not just that they expect people to plow the money back in, but that pros have to wait for fish to plow money in to get to the +EV situation.
The difference with blackjack is that you can (in theory) adjust your bet to take advantage of the different phases of blackjack. Your first sentence seems to match Roland's comment about the Kelly criterion (you lose betting against snake eyes if you bet your whole bankroll every time), but that doesn't make sense with fixed-bet slots. There, if it made sense to make the first bet, it makes sense to continuing betting after a jackpot.
To whom it may concern:
This thread is for the discussion of Less Wrong topics that have not appeared in recent posts. If a discussion gets unwieldy, celebrate by turning it into a top-level post.
(After the critical success of part II, and the strong box office sales of part III in spite of mixed reviews, will part IV finally see the June Open Thread jump the shark?)