@Will
From a lender's perspective, a property is worth what it sells for. It doesn't matter what the comps come in at if the property is selling for less. If you buy a property for 60k, it is worth 60k because nobody is willing to pay more for it. If there was someone willing to pay 65k for it, why would someone sell it to you for 60k (unless the property isn't on the open market).
There are also different investment vehicles for the stock market that do allow purchases at values other than market. Options contracts are one such vehicle.
The stock market also allows investors to sell short. Although it is risky, tons of money can be made by betting on a stock going down. This is a strategy that I cannot see a comparison available in RE.
Taking it further, in the FX market (I know that this isn't stock), you can employ leverage (a favorite strategy by many on this board) like nowhere else. Again, it is very risky, but you can leverage your money over 100x in some instances (depending on your investment among other things). Its nice to come to the table with 10k, and be able to invest 1MM worth.