Exponential growth is also expected within new businesses within an established corporation. Similar to software's margins and distribution advantage, an existing corporation can often pursue new businesses with an existing infrastructure that approaches minimal additional expense beyond human salaries. The reference to "hurdle rate" is an often used term by corporate MBAs evaluating the worth of a new line of business.
A business that’s shrinking but throwing off cash is with a lot still. Only the valuation multiple is based on growth.
Exponential growth is expected in startups of all industries, software only makes the margins and distribution easier.