I'll add that we expect software to work on highly heterogeneous systems, too. If you're working on a bridge, you known exactly the terrain you're required to

I'll add that we expect software to work on highly heterogeneous systems, too. If you're working on a bridge, you known exactly the terrain you're required to span. The engineers battle with a lot of integration issues, but at least they know what they're dealing with. With software development, well, who's to say what integration issues that millions of people might face?