I don't think that is a fair assessment of the situation. While some people may be in a position where getting laid off from their job is a welcomed incentive to pursue bigger and better things, there are also those people that rely on that steady income to pay their bills and keep their families clothed, fed, educated, and healthy.
I also want to say, although I don't mean to imply that this was your personal assumption, that not every person working for a technical company in the valley is a risk taking entrepreneur. Some people just like to program.
I expect they're also targeting a lot of senior (read: high-salary) employees who are more likely to be the family bread-winner types. (Although for legal reasons Yahoo! will go to great pains to point out that they are not in any way targeting older employees.)
I also want to say, although I don't mean to imply that this was your personal assumption, that not every person working for a technical company in the valley is a risk taking entrepreneur. Some people just like to program.