I think the issue is that a larger number of people are becoming involuntary entrepreneurs. They don't want the long-term "lifestyle" business that delivers a high-but-not-stratospheric income for 20 years, because they actually aren't cut out for running businesses (or very interested in it). They want the 5-year plan to exit-- because they're not really entrepreneurs, but either (a) want to be rich, or (b) want autonomy that no longer exists in any corporate job-- not even R&D. They're involved in these red-ocean VC-funded get-big-or-die gambits because those are the only game in town for them.

In 2006, class (a) was working on Wall Street; but the pool of get-rich opportunities has dwindled. In 1975, class (b) was working in R&D labs on basic research. However, those options have dwindled too. As the few buttresses preventing the corporate world from falling under the weight of its own mediocrity give way, it's forcing a lot of the best people into one narrowly-defined class of entrepreneurship: VC-funded turn-the-crank franchise bids with a bit (ok, a lot) of random risk thrown in. It ends up requiring long hours, alternating unhealthfully between being over- and under-funded (relative to one's scope) and is generally unsustainable. Many of these people can't hack it for more than a couple years; that's why the acq-hires are so necessary-- turn the business over to something that can use it prophylactically before the founders burn out.