When calculating how much your buddy spent on his bike, use the Rule of Three popularized by "American Pie." Whatever he says, multiply it by three to get the real answer. And you know what? Good for him! You wouldn't ask if you weren't drooling. So why, then, would you turn around and leave it out in the open for anyone to get their hands on it? It doesn't matter how much you needed that post-ride pint, making the solo walk home in a cycling kit sans bike probably isn't the look you were going for.
As for leaving your bike outside for long periods of time, it's basically the same as putting it away dirty. Snow, rain and grime can accumulate on the pieces and parts, causing rust and other unwanted things to occur.