I don't read this as when open-source was invented, but when it happened for the corporate world. In 2002 it was a very reasonable choice for $BIG_COMPANY to use a proprietary web server, e.g. IIS. In 2008 that would have been really be weird.
In the 90s windows was shipping with components cribbed from open source (and properly attributed).
It's not something new.
But why did that make development cheaper? An enterprise copy of Windows with IIS cost maybe a thousand bucks, right? Maybe there were more costs, my knowledge is, y'know, 23 years out of date.