Safari runs on the Webkit engine. In Mac OS X, the only way that you can change your default browser in through the Safari preferences pane, which I assume is what sirena is seeing, just left over from the Windows port.
I'd like to see a screen of how the NY Times page is beings garbled. Safari on Mac usually doesn't have CSS problems, and I'd hate to start hacking for another browser. I hope that Apple didn't open a can of worms with this rather unnecessary move.