Short sales have come into favor a lot in the recent 2 years, which are basically pre-foreclosures.
The problem with trying to buy a house from a homeowner who is underwater for 35% under market is that in most cases, the deal simply can't come together. It's not like the person has 35% equity but can't make the payments, in most cases, they've got less than 10% (or 5%) equity.
Case in point: Overeager homeowner bought House A in 2007 for $450k. Because of the down market, that house is now worth $400k. Traditionally, a bank would have required a 20% downpayment (80/20LTV) to secure the investment. However, as of late, thanks in part to Barney "Lend to Everyone" Frank and Chris "It has a pulse? Fund it!" Dodd, people could get 100% financing. In some cases, they could get 104% of the house's value.
So now, overeager homeowner, who barely had a downpayment, and made interest only payments, now has a loan balance of $420k on a house that would now go for $400k. Selling at market value isn't even an option (because the loan balance exceeds the market value), let alone selling below market so an investor can make money on the back end.
You're right in the sense that you need cash to make deals like this work. Thanks to short sales, many banks are allowing properties to be sold "short" of their loan balances. It is a cumbersome, slow moving process however, and having cash can only get you so far. Because people so overpaid for houses and put so little money down, there is often a wide margin between the profit generating numbers an investor wants to see, and loan balance that the homeowner/lender must fulfill.
PS- In most cases with short-sales and serious mortgage delinquency, people's credit isn't "saved." It's severely dinged at best. There really is no rosy outlook on the real estate situation of the last couple of years. Hopefully as things mend, some of the ugliness will go away. Being that the current administration won't face the realities of the impetus for the housing collapse, that ugliness is likely to hang around for a bit.
"The first lesson of economics is scarcity: there is never enough of anything to fully satisfy all those who want it. The first lesson of politics is to disregard the first lesson of economics." Thomas Sowell