Stocks are much easier to repossess and liquidate during a margin call which results in margin interest being lower than mortgage interest. You can't get as much leverage as you can with real estate but that's because of government regulation not because banks are unwilling.
From most brokers, margin rates are higher rate than mortgage financing. Etrade, Fidelity, Schwab, Merrill, Scottrade, Ameritrade, Vanguard are all (much) higher than mortgage rates right now.
Some deep discount houses (IB and TradingDirect among likely some others) are lower than mortgage rates.
Stocks are much easier to repossess and liquidate during a margin call which results in margin interest being lower than mortgage interest. You can't get as much leverage as you can with real estate but that's because of government regulation not because banks are unwilling.