Getting locked into free software like PostgreSQL is a lot less risky than getting locked into a proprietary system whose owner could gouge you or evict you at your most vulnerable moment.
Exactly. There's slmost no comparison given a proprietary company can straight-up tell you "No, we will no longer sell you the product even if you will pay big $$$ for it. "
Not theoretical: Microsoft, Borland, IBM, HP, Oracle/Sun... all did it at least once with Microsoft doing it many times. They're not open, which drives up the cost of exiting dramatically.
