pg: i agree once again.
the exogenous nature of technological progress has always been independent of GDP growth. When the economy grows and consumption is booming, tech firms and start-up founders benefit yes, but then it's like waiting for a sunny day to go for a walk.
You could go for a walk any day and get the same benefits: exercise and sight-seeing. In fact, too much sun might hurt you but you could always learn to get creative against wind/rain (coat and umbrella).
I guess what I'm saying here in case you're lost is that a recession is bad weather than need not distract tech start-ups from flexing their muscles. If you could make it in bad weather, chances are, you could enjoy more success in the sunny weather!
I don't want to say I agree that one has to launch a start-up during recessions only. Obviously, the most ideal time to start one is to know you can make decent money and a product that solves an important problem, be it in a good or bad economy, because, statistically, recessions are shorter and milder than before and expansions longer.
In the end, it is not a question of when, even. It remains a question of how.