Other people in this thread report that Schwab pays interest on checking account balances. Schwab's website clearly states that their checking account accrues interest. There's a footnote link there, but the fine print simply says that the rate can change over time.
https://www.schwab.com/public/schwab/banking_lending/checkin...
Of course, just as I don't understand people using a traditional bank these days, I likewise don't understand letting a large cash balance sit in checking account. The best interest rate you're going to see these day is probably sub-1%.
So why leave excess money sitting around in a checking account, when sweeping it into even a short-term U.S. bond fund would provide 2x-10x the return with no additional risk? (i.e. if U.S. Treasuries default, then money market accounts are probably screwed too anyway)
Of course, interest rates are currently so low that it's basically a moot point. And I hardly ever have let any idle cash sit around without sweeping it into a short-term bond fund, or something better than the money market default.